저 시-비 리- 경 지 2.0 한민

는 아래 조건 르는 경 에 한하여 게

l 저 물 복제, 포, 전송, 전시, 공연 송할 수 습니다.

다 과 같 조건 라야 합니다:

l 하는, 저 물 나 포 경 , 저 물에 적 된 허락조건 명확하게 나타내어야 합니다.

l 저 터 허가를 면 러한 조건들 적 되지 않습니다.

저 에 른 리는 내 에 하여 향 지 않습니다.

것 허락규약(Legal Code) 해하 쉽게 약한 것 니다.

Disclaimer

저 시. 하는 원저 를 시하여야 합니다.

비 리. 하는 저 물 리 목적 할 수 없습니다.

경 지. 하는 저 물 개 , 형 또는 가공할 수 없습니다.

i

Abstract

Inspired from microstructure-based reversible fastening mechanisms in

biological system, a number of researches have been conducted to elucidate

the principle of adhesion and to mimic its function. Structures with high

aspect ratio have been desirably used to maximize van der Waals force,

though the weakness of the structures has been one of the major huddles for

practical use. Here, instead of high aspect ratio structures which are

vulnerable to mechanical failure, the interlocking between arrays of regularly

protruded line structures is introduced to provide remarkable repeatability

while maintaining substantial adhesion force. Mechanical interlocking

between line arrays made by UV-curable material is mediated by van der

Waals interaction when two surfaces are brought into contact. By optimizing

the geometry and material, ‘failure-free’ working condition is established and

maximum measured adhesion force is recorded about ~ 29.6 N/cm2 without

any degradation in adhesion force during repeatable attachment. To analyze

the adhesion characteristics, a theoretical model is established using

Timoshenko beam bending theory and van der Waals interaction between two

surfaces with nanoscale roughness.

Keywords : biomimetics, reversible interlocking, line array

structure, dry adhesive, van der Waals force

Student Number : 2012-22563

ii

Contents

Abstract i

Nomenclature iii

List of Figures iv

1. Introduction 1

2. Experimental Results

2.1. Fabrication of PUA line arrays

2.2. Adhesion measurements

2.3. Repeatability test

5

6

9

3. Analysis

3.1. Beam deflection analysis

3.2. Van der Waals force analysis and combined modeling

12

14

4. Conclusion 17

Experimental Section

Figures

References

19

21

29

Abstract (Korean) 33

iii

Nomenclature

λ

E

𝑃𝑐

𝐼

𝐿

𝜎𝑏

𝑀𝑏

𝑦

𝑀

G

𝜈

𝜅

𝛿

𝜎

Wavelength of light

Elastic modulus (Young’s modulus)

Critical buckling load

Second moment of inertia

Height of the line structure

Bending stress of the structure

Bending moment of the structure

Distance from the neutral axis

Deflection of the beam

Bending moment of the beam

Shear modulus

Poission’s ratio

Cross-sectional area

Shear correction coefficient

Deflection length

Hamaker constant

Cut-off distance

Probability of area in contact

Surface energy

RMS roughness of the surface

Friction coefficient

Bending angle

iv

List of Figures

Figure 1. (a) Fabrication process of a PUA line array by two-step

molding method. (b) Schematic illustration of the interlocking

procedure. (c) Cross-sectional SEM image of interlocked line

array.

Figure 2. (a) SEM images of the nanoscale line array (width = 800 nm)

with three different spacing ratios (1, 3, and 5). The inset

shows bird-view of the each array. (b) Measured normal and

shear adhesion force of samples.

Figure 3. (a) SEM images of the line structure array with three different

feature sizes (400 nm, 800 nm, and 5 μm). The inset shows

bird-view of the each array. (b) Plots showing a growing

tendency of the adhesion force as pattern size increases. (c-d)

Macroscopic locking status and corresponding cross-sectional

SEM images of (c) 800 nm feature size and (d) 5um feature

size.

Figure 4. Adhesion graph showing normal and shear adhesion forces

with different materials.

Figure 5. (a) Measurement of adhesion forces with repeating cycles of

attachment and detachment up to ~250 cycles of normal

v

direction and ~100 cycles of shear direction. (b) SEM images

of a pristine line array sample and the same after normal and

shear repeatability test. (c) Two representative failure modes

of the protruded structure with different types of external

loads.

Figure 6. (a) Schematic illustration of the deflection and force

equilibrium of the interlocked structure. (b) 3-D AFM image

showing the nanoscale roughness on the surface of the pattern.

(c) Optical microscope images of the interlocked line array,

showing that locked and unlocked region is coexisted. (d)

Plots of expected shear adhesion force predicted by two types

of beam bending theories and measured adhesion force that

follows Timoshenko beam bending theory.

Figure 7. Photographs of a custom-built equipment used to measure the

normal and shear adhesion force of samples. A load cell is

installed for each direction and the pulling force is applied by

motorized moving part.

1

1. Introduction

2

Reversible fastening and fixation ability is known as one of the crucial

requirements for the survival of a number of species in nature, which can be

realized by various systems including mechanical, electrochemical, and

capillary-based principles.[1-3]

Structure-based locking apparatus has been

widely employed for various species, for example, the hook structure of the

plants,[4,5]

interlocking system of dragonfly’s head arrester[6]

and wing locking

system in beetles.[7]

Recently, a gear-like structure was found in plant hoppers,

which enables synchronized movements of each leg for the jumping process.[8]

Inspired from aforementioned biological system, there have been

many attempts to take advantage of structure-based mechanical locking

effects realized by various shapes and materials such as core-shell nanowire

forest,[9,10]

carbon nanotubes (CNTs),[11,12]

polymer nanofibers,[13,14]

sharp

particles,[15]

and rippled structure.[16-18]

In these cases, the attractive van der

Waals force plays a key role to exert stable adhesion. It has been known that

the structures with high aspect ratio (HAR) are desirably used to maximize the

van der Waals effect by providing larger surface area. A wide variety of

valid results have presented theoretical prediction.[13,19]

However, due to its intrinsic mechanical instability, HAR structures

are vulnerable to irreversible buckling, mating, and lateral collapsing when

external load is applied or the structures are contacted with each other.[20,21]

Though damaged structures of biological organisms, which consist of β-

keratin can be easily regenerated, synthetic HAR fibers cannot recover its

original shape after mechanical failures.[13,14,22]

Such unstable characteristic of

HAR structures is one of the major obstacles for a repeatable and practical

attachment system.

3

Therefore, the realization of the repeatable high adhesion system by

mechanically stable structures is highly demanded for the practical application

of dry adhesive system. Here, protruded line array structures with relatively

low AR (~2) and wide pattern provide greater structural stability than HAR

features. Based on mechanical robustness, line interlocking system shown

here exerts exceptionally high repeatability while maintaining its strong

adhesion forces both in the normal and shear direction. Also, line arrays are

easily replicated using ultraviolet (UV) curable materials that may enable

large area fabrication. In this paper, the ideal condition of interlocking with

line arrays is presented in terms of geometric and material aspects, compared

with the case of HAR fibers. Also, a theoretical model for the present system

is established using Timoshenko beam bending theory and van der Waals

interaction.

4

2. Experimental results

5

2.1. Fabrication of PUA line arrays

The entire fabrication process of line array structures by UV-curable material

is summarized in Figure 1(a). First, the silicon masters engraved with various

types of line arrays were fabricated by conventional photolithography and

deep reactive ion etching (DRIE) process. The surface of the master mold is

treated with octafluorocyclobutane (C4F8) gas in the inductively coupled

plasma (ICP) chamber for the easy detachment of polymers.

To fabricate the 1st replica, polydimethylsiloxane (PDMS) precursor

mixed with 10 wt% of curing agent (Sylgard 184, Dow Corning) was poured

onto the silicon mold. After degassing process in a vacuum chamber, it was

cured at 70℃ for 1 hour and the PDMS replica was carefully peeled off from

the silicon master mold. . This series of process can be repeated several times

to make multiple replica molds. After that, two types of PUA prepolymers (s-

PUA; PUA MINS 311 RM, h-PUA; PUA MINS 301 RM, purchased from the

Minuta Tech, Korea) were prepared for the UV molding process to make the

2nd replica. A drop of PUA was dispensed onto the master mold and a

polyethylene terephthalate (PET) film (50 μm thickness) was slightly pressed

against the liquid drop for it to be used as a supporting layer. The precursor

was exposed to UV light (λ=250-400 nm, intensity of ~100 W/cm2, Fusion

Cure System, Minuta Tech, Korea) during the curing time about ~60 seconds.

After exposure, it was detached from the PDMS mold by peeling off the

substrate, followed by additional exposure to UV light for several hours for

complete curing.

6

2.2. Adhesion measurements

Figure 1(b) shows an illustration of the interlocking procedure between as-

made line array structures, and corresponding cross-sectional image is shown

in Figure 1(c). Before initial contact, the upper and lower line array structure

samples should be aligned to secure parallel state. When the locking is

initiated at one side, sequential locking is triggered by pressing the sample

towards the other side. This line-to-line locking process is analogous to the

fastening procedure of conventional zipper in the way that complementary

structure is clasped with each other by external load.

To find out the optimal geometry of this ‘zipper-like’ contact, a series

of experiments were conducted. First, the adhesion test about line arrays with

several sets of different spacing ratio (SR, defined as line spacing/line width)

was conducted to find out which one would be the most effective condition

for interlocking phenomena. For each case, the width of individual line

structure is fixed as 800 nm (Figure 2(a)). The result shown in Figure 2(b)

indicates that in the case of SR of 3 and 5, both normal and shear adhesion

force is comparable or even less than flat-to-flat adhesion (~2.3 N/cm2 for

normal and ~8.6 N/cm2 for shear direction), whereas the significant increase

in adhesion force is observed in the case of SR=1 (~ 6.1 N/cm2 for normal and

~15.7 N/cm2 for shear). In short, smaller spacing ratio is more advantageous

because of not only larger contact surfaces but also more probability of

contact caused by the narrowed spacing between adjacent structures. This

tendency is truly distinguishable, given that interlocking between HAR hairy

structures is hard to occur for the case of SR≅1, especially attributed to the

buckling of the structure.[14]

7

Next, to find out the relationship between the pattern size and

adhesion force, adhesion tests were performed with three different samples

(Figure 3(a)). Interestingly, it is found that there is a monotonic increment in

adhesion force as the width of the line structure feature becomes larger. In the

case of HAR hairs, the contacted area of interlocked hairs is directly

proportional to the density of hair array and thus the smaller the hair feature

size, the greater the adhesion force[13]

. However, when employing the line

structure, both maximum normal (~8.5 N/cm2) and shear (~29.6 N/cm

2)

adhesion force is measured when the width of structure is 5 μm (Figure 3(b)).

This phenomenon can be explained by the difference in the macroscopic areal

fraction of interlocked region. As seen in Figure 3(c), in the case of nanoscale

line array, the complete locking region is distinguishable by naked eye since

the region becomes optically transparent as the spacing is completely filled

with the counterpart. The picture shows that fully locked region is sparsely

scattered over the entire area, which leads to the loss of adhesion force. This is

attributed to the fact that it is very tricky to align the array consisting of

nanoscale feature. The perfect alignment of nanoscale line array is beyond the

level of manual manipulation by hand. On the other hand, microscale array

shows uniform locking for the entire area (Figure 3(d)) thereby providing

stronger adhesion. One thing to note is that even for the case of SR=1, the

width of the spacing should be slightly wider than the width of the line

structure (SR of ~1.2 is used in this paper) to maintain clearance fit condition,

unless interlocking does not occur since the structures are hardly fitted into

the space.

Aside from geometrical aspects, the effect of elastic modulus of

8

building material was investigated. The elastic modulus (denoted as E) of

PUA material can be tuned by changing the component and ratio of modulator,

which has been reported in earlier reports.[23,24]

In this experiment, two types

of UV-curable materials were used: s-PUA (E=19.8 MPa) and h-PUA (E=320

MPa). The geometry of the samples is fixed as width of 800 nm and SR of 1.

The result shows that structures with s-PUA present higher adhesion force

than h-PUA structures (Figure 4), which is consistent with previous

experimental results[13]

. The reason for the higher adhesion force in softer

material can be explained in terms of the probability of conformal contact

with the nanoscale roughness, which is discussed in the following section.

9

2.3. Repeatability test

To demonstrate the durability of the interlocking system, 250 cycles and 100

cycles of the normal and shear attachment test were conducted, respectively

(Figure 5(a)). As seen, no sign of degradation in normal and shear adhesion

force is observed throughout the experiment, and the structural rigidity is also

verified by the SEM image after the test (Figure 5(b) and (c)). It is notable

that such robust adhesion is achieved without any surface modification such

as coating with metals[13,22,25]

. To elaborate the remarkable durability of line

structure compared with HAR hairs, a simple theory is introduced. For the

case of a long-term repeatable adhesion, failures of protruded structure can

happen in the form of two cases depending on the direction of external load

depicted in Figure 5(d): i) buckling of structure due to normal load, and ii)

fracture at the bottom induced by tensile bending stress.

In the case of buckling, it would happen when the paired structure is

faced each other at the top surface and squashed by pressing force. Assuming

clamped end at the bottom and hinged end at the top side, critical buckling

load (𝑃𝑐) of the single structure can be expressed as[26]

𝑃𝑐 = 20.2𝐸𝐼

𝐿2

where 𝐼 is the second moment of inertia and 𝐿 is the height of the structure,

respectively. After calculating 𝑃𝑐 of the individual unit, macroscopic critical

pressure can be calculated by considering the areal density of the array. When

considering the micro-scale line structure used in Figure 5 (width=5 μm,

SR=1, and AR=2), critical buckling pressure is estimated as 3.3 MPa (=330

10

N/cm2), which is far beyond the range of applied preload (~10 N/cm

2). But in

the case of the polymeric hairy structure, both SR and AR needs to be higher

than this value (SR of ~3 and AR of ~10[13,14,27,28]

) to raise the probability of

contact and amplify surface contact area for significant decrease in the critical

buckling pressure.

Also, bending stress should be considered to figure out whether the failure of

the structure would happen. In the case of the bending of the cantilever, the

stress caused by the applied bending moment, 𝜎𝑏, can be expressed as[26]

𝜎𝑏 =𝑀𝑏𝑦

𝐼

where 𝑀𝑏 is the bending moment at the section and 𝑦 is the distance from

the neutral axis, respectively. According to the measured shear adhesion force

and the assumption of distributed load condition, calculated average bending

stress at the bottom of the structure is about 4.5 MPa which is half of the

ultimate tensile stress of the s-PUA (~9 MPa[23]

).

Consequently, the failure of the whole line structure is hardly expected during

the regular attachment and detachment process, except for gradual surface

abrasion due to sliding between contact surfaces.

11

3. Analysis

12

3.1. Beam deflection analysis

To analyze the measured adhesion force induced by interlocking of line arrays,

Timoshenko beam theory is introduced to model the line structure as a thick

beam. It is generally acknowledged that Timoshenko beam theory is more

appropriate to explain the deformation of the beam than the simple beam

theory (also known as Euler-Bernoulli beam theory) when the thickness of the

beam is considerably larger than the length of the beam (i.e. low AR), since

the transverse shear deformation should be considered in that case.[29-31]

In

the case of implementing Timoshenko beam theory, the amount of the

deflection of the beam can be expressed as the combination of the deflection

predicted by the simple beam theory and additional term induced by

transverse shear force.[30]

With the boundary condition of clamped end at the

base and free end at the tip of the structure, deflection of the beam can be

denoted as

=

(

where denotes the deflection, 𝑀 is the bending moment, 𝑀 is the

bending moment at the base, G is the shear modulus (G =

2 1+𝜈 , 𝜈 is the

Poisson’s ratio), A is cross-sectional area, 𝜅 is the shear correction

coefficient (𝜅 = + 𝜈

+ 𝜈 for rectangular cross-section

[32]) and superscript T

and E indicates the corresponding term belongs to the Timoshenko beam

theory and Euler-Bernoulli beam theory.[30]

13

When the external load is induced by shear loading and the uniform load

distribution across the contact area is assumed, the deflection at the tip 𝛿𝑚𝑎𝑥

can be expressed as

𝛿𝑚𝑎𝑥 = 2 𝐿 (

𝐿2

𝐸𝐼

( )

2

𝜅 )

where is the applied shear force per single structure and is the overlap

ratio ( =𝑏

), respectively (Figure 6(a)). From experimental observations, the

average value of is estimated as 0.8. After all, the amount of the deflection

can be expressed as the function of the external shear force and overlap ratio.

14

3.2. Van der Waals force analysis and combined modeling

When the two line structures are brought into contact, van der Waals

interaction occurs at the contact surface and the van der Waals force per unit

area can be written as [33]

=

where denotes the Hamaker constant and is the cut-off distance

between surfaces which is assumed to be 0.4 nm.[33,34]

One thing to note is the

equation is based on the assumption that both two surfaces are nominally flat.

However, nanoscale roughness on the contact surface needs to be considered

because only a small amount of roughness can significantly affect the

variation of adhesion force.[34-37]

According to the previous researches, many

types of surface roughness can be modeled as a Gaussian distribution of

asperity heights.[38,39]

Also, contact between two rough surfaces can be

replaced as that of one nominally flat surface and one rough surface with

combined roughness.[40,41]

Then, the probability of area in contact between the

two identical surface, , can be derived as

=

2[ (

𝛿1 𝛿2 𝑚

2𝜎) (

𝑚

2𝜎)]

where erf denotes the error function, 𝛿1 = . 2𝜎1 2 𝜈2 𝐸 2

and 𝛿2 = 2. 2𝜎1 2 𝜈2 𝐸 2 is the minimum and maximum

amount of deformation predicted by Johnson-Kendall-Roberts (JKR) contact

15

model ( is the surface energy of s-PUA(=32.8 mJ/m2)

[42]), 𝜎 is the RMS

roughness of surface, 𝑚 is the maximum height of peak for the contacting

surface (approximated by 2.7 𝜎), (detailed derivation is shown in Ref.[40]

).

After substituting the measured value of 𝜎 (2.2 nm, Figure 6(b)), the value of

in the case of s-PUA is calculated to about 97 %, indicating that almost the

entire area is contacted with each other. However, this value falls into 15 %

when the contact of structure is made by h-PUA. It means the assumption of

the conformal contact is no longer valid, leading to lower adhesion force of h-

PUA surface as shown in Figure 4.

By applying revised van der Waals force which takes into account

nanoscale surface roughness and assuming the law of friction as (F = μN),

force equilibrium equation at a pair of interlocked line array is established

(Figure 6(a)). As shown, the interlocked line structure maintain the merged

state until

Where is the external shear force applied to the single structure, is

the van der Waals force at the contact surface, respectively. The paired

structure would begin to be separated when the inclined angle reaches critical

value ( 𝑐) that satisfies

𝑐 = 𝑐

from geometric approximation, 𝑐 𝛿𝑚𝑎𝑥 𝐿. By substituting 𝛿𝑚𝑎𝑥 to the

above force equilibrium equation, can be calculated. Then, the

macroscopic adhesion force can be estimated by multiplying the number of

paired structures per unit area. Since some portion of the array cannot be

16

interlocked due to uneven substrate, misalignment, and contaminants (e.g.

dust particles) (Figure 6(c)), the adhesion force of the whole system is

influenced by the locking ratio. In Figure 6(d), both Euler-Bernoulli and

Timoshenko beam bending theory predicts a monotonic increase in adhesion

force related with the locking ratio. Experimental results of adhesion force

with changing the locking ratio showed large discrepancy to the theoretical

value based on Euler-Bernoulli beam bending theory, while well matched to

the Timoshenko beam bending theory. This result shows the importance of

adopting the large deformation theory when considering the deflection of

relatively low AR structures.

17

4. Conclusion

18

A reversible interlocking system using regularly arrayed line array structure

has been presented. It can be fabricated by the simple UV-assisted molding

method. Designing rules for providing high adhesion force has been

investigated in terms of geometrical aspect and material characteristics. By

utilizing its structural robustness, long-term operation with repeatable

attachment and detachment was achieved without any notable degradation in

adhesion force. Also, a theoretical analysis using Timoshenko beam bending

theory and van der Waals force with nanoscale roughness has been conducted

to explain measured adhesion force. With further optimization based on the

analysis shown here, it might be possible to further enhance the performance

of the current line interlocking system.

19

Experimental section

20

Adhesion test

The adhesion test was conducted by the custom-built equipment (Figure 7). In

the measurement machine, the normal and shear adhesion force is measured

by load cell attached to each direction. The pre-aligned sample was loaded at

the flat stage and a preload of ~ 10 N/cm2 was applied. The adhesion force

was measured at least 10 times for each case and the averaged value was used.

Also, the measured adhesion value was divided by actual contact area to

calculate adhesion force per unit area (N/cm2). During the measurements, the

temperature of the stage was maintained at 20 ℃ and the relative humidity of

ambient was about 50%.

Field-Emission Scanning Electron Microscopy (FE-SEM)

SEM images were obtained by Auriga (Carl Zeiss, Germany) and S-4800

(Hitachi, Japan). To avoid charging effects, samples were coated with a Pt

film about ~ 5 nm thickness prior to measurements.

Atomic Force Microscopy (AFM)

AFM images were taken by a XE-150 (Park Systems, Korea) in noncontact

mode. The scan rate was 0.6 Hz and scan resolution was 256 x 256 pixels.

21

Figures

22

Figure 1. (a) Fabrication process of a PUA line array by two-step molding

method. (b) Schematic illustration of the interlocking procedure. (c) Cross-

sectional SEM image of fully interlocked line array.

23

Figure 2. (a) SEM images of the nanoscale line array (width=800 nm) with

three different spacing ratios (1, 3, and 5). The inset shows bird-view of the

each array. (b) Measured normal and shear adhesion force of samples.

24

Figure 3. (a) SEM images of the line structure array with three different

feature sizes (400 nm, 800 nm, and 5 μm). The inset shows bird-view of the

each array. (b) Plots showing a growing tendency of the adhesion force as

pattern size increases. (c-d) Macroscopic locking status and corresponding

cross-sectional SEM images of (c) 800 nm feature size and (d) 5um feature

size.

25

Figure 4. Adhesion graph showing normal and shear adhesion forces with

different materials.

26

Figure 5. (a) Measurement of adhesion forces with repeating cycles of

attachment and detachment up to ~250 cycles of normal direction and ~100

cycles of shear direction. (b) SEM images of a pristine line array sample and

the same after normal and shear repeatability test. (c) Two representative

failure modes of the protruded structure with different types of external loads.

27

Figure 6. (a) Schematic illustration of the deflection and force equilibrium of

the interlocked structure. (b) 3-D AFM image showing the nanoscale

roughness on the surface of the pattern. (c) Optical microscope images of the

interlocked line array, showing that locked and unlocked region is coexisted.

(d) Plots of expected shear adhesion force predicted by two types of beam

bending theories and measured adhesion force that follows Timoshenko beam

bending theory.

28

Figure 7. Photographs of a custom-built equipment used to measure the

normal and shear adhesion force of samples. A load cell is installed for each

direction and the pulling force is applied by motorized moving part.

29

References

30

[1] M. Scherge, S. N. Gorb, H. A. Stone, Physics Today 2002, 55 (6), 53.

[2] S. N. Gorb, Philos. Trans. R. Soc., A 2008, 366 (1870), 1557-1574.

[3] B. Bhushan, Philos. Trans. R. Soc., A 2009, 367 (1893), 1445-1486.

[4] K. Koch, B. Bhushan, W. Barthlott, Prog. Mater. Sci. 2009, 54 (2), 137-

178.

[5] M. W. Szyndler, K. F. Haynes, M. F. Potter, R. M. Corn, C. Loudon, J. R.

Soc., Interface 2013, 10 (83).

[6] S. N. Gorb, Proc. R. Soc. B 1999, 266 (1418), 525-535.

[7] S. N. Gorb, Int. J. Insect Morphol. Embryol. 1998, 27 (3), 205-225.

[8] M. Burrows, G. Sutton, Science 2013, 341 (6151), 1254-1256.

[9] H. Ko, Z. Zhang, J. C. Ho, K. Takei, R. Kapadia, Y.-L. Chueh, W. Cao, B. A.

Cruden, A. Javey, Small 2010, 6 (1), 22-26.

[10] H. Ko, J. Lee, B. E. Schubert, Y. L. Chueh, P. W. Leu, R. S. Fearing, A.

Javey, Nano Lett. 2009, 9 (5), 2054-2058.

[11] V. P. Veedu, A. Cao, X. Li, K. Ma, C. Soldano, S. Kar, P. M. Ajayan, M. N.

Ghasemi-Nejhad, Nat. Mater. 2006, 5 (6), 457-462.

[12] K. P. Yung, J. Wei, B. K. Tay, Diamond Relat. Mater. 2009, 18 (9), 1109-

1113.

[13] C. Pang, T.-i. Kim, W. G. Bae, D. Kang, S. M. Kim, K.-Y. Suh, Adv. Mater.

2012, 24 (4), 475-479.

[14] C.-M. Chen, C.-L. Chiang, C.-L. Lai, T. Xie, S. Yang, Adv. Funct. Mater.

2013, 23 (30), 3813-3823.

[15] X. Jin, J. Strueben, L. Heepe, A. Kovalev, Y. K. Mishra, R. Adelung, S. N.

Gorb, A. Staubitz, Adv. Mater. 2012, 24 (42), 5676-5680.

[16] S. Vajpayee, K. Khare, S. Yang, C.-Y. Hui, A. Jagota, Adv. Funct. Mater.

2011, 21 (3), 547-555.

[17] E. P. Chan, E. J. Smith, R. C. Hayward, A. J. Crosby, Adv. Mater. 2008,

20 (4), 711-716.

[18] P.-C. Lin, S. Vajpayee, A. Jagota, C.-Y. Hui, S. Yang, Soft Matter 2008,

4 (9), 1830-1835.

[19] R. M. McMeeking, L. Ma, E. Arzt, J. Appl. Mech. 2009, 76 (3), 031007-

031007.

31

[20] C. Greiner, A. del Campo, E. Arzt, Langmuir 2007, 23 (7), 3495-3502.

[21] N. J. Glassmaker, A. Jagota, C.-Y. Hui, J. Kim, J. R. Soc., Interface 2004,

1 (1), 23-33.

[22] T.-i. Kim, H. E. Jeong, K. Y. Suh, H. H. Lee, Adv. Mater. 2009, 21 (22),

2276-2281.

[23] P. J. Yoo, S.-J. Choi, J. H. Kim, D. Suh, S. J. Baek, T. W. Kim, H. H. Lee,

Chem. Mater. 2004, 16 (24), 5000-5005.

[24] S.-J. Choi, H. N. Kim, W. G. Bae, K.-Y. Suh, J. Mater. Chem. 2011, 21

(38), 14325-14335.

[25] H. Yoon, M. K. Kwak, S. M. Kim, S. H. Sung, J. Lim, H. S. Suh, K. Y. Suh,

K. Char, Small 2011, 7 (21), 3005-3010.

[26] S. H. Crandall, T. J. Lardner, N. C. Dahl, An introduction to the

mechanics of solids. McGraw-Hill Book Company: 1999.

[27] C. Pang, D. Kang, T.-i. Kim, K.-Y. Suh, Langmuir 2011, 28 (4), 2181-

2186.

[28] H. Shahsavan, B. Zhao, Langmuir 2011, 27 (12), 7732-7742.

[29] S. Timoshenko, S. Timoshenko, J. Goodier, Theory of Elasticity, by S.

Timoshenko and JN Goodier. McGraw-Hill Book Company: 1951.

[30] C. Wang, J. Eng. Mech. 1995, 121 (6), 763-765.

[31] P. Du, I.-K. Lin, H. Lu, X. Zhang, J. Micromech. Microeng. 2010, 20 (9),

095016.

[32] T. Kaneko, J. Phys. D: Appl. Phys. 1975, 8 (16), 1927.

[33] D. Leckband, J. Israelachvili, Q. Rev. Biophys. 2001, 34 (02), 105-267.

[34] Y. I. Rabinovich, J. J. Adler, M. S. Esayanur, A. Ata, R. K. Singh, B. M.

Moudgil, Adv. Colloid Interface Sci. 2002, 96 (1–3), 213-230.

[35] K. N. G. Fuller, D. Tabor, Proc. R. Soc. London, Ser. A 1975, 345 (1642),

327-342.

[36] D. Tabor, J. Colloid Interface Sci. 1977, 58 (1), 2-13.

[37] R. P. Jaiswal, G. Kumar, C. M. Kilroy, S. P. Beaudoin, Langmuir 2009, 25

(18), 10612-10623.

[38] M. Nosonovsky, B. Bhushan, Adv. Funct. Mater. 2008, 18 (6), 843-855.

[39] J. A. Greenwood, J. B. P. Williamson, Proc. R. Soc. London, Ser. A 1966,

32

295 (1442), 300-319.

[40] S. You, M. P. Wan, Langmuir 2013, 29 (29), 9104-9117.

[41] P. Prokopovich, V. Starov, Adv. Colloid Interface Sci. 2011, 168 (1–2),

210-222.

[42] M. K. Kwak, T.-i. Kim, P. Kim, H. H. Lee, K. Y. Suh, Small 2009, 5 (8),

928-932.

33

요 약

본 논문은 자연계에 존재하는 다양한 생명체에서 찾아볼 수 있는

미세구조 기반의 가역적 상호체결 시스템에 대한 연구로, 자외선

경화성 고분자를 이용하여 제작된 선형 구조물 배열간의 상호체결

현상에 대한 연구를 수행하였다. 기존의 고종횡비 기둥 구조물 기반

상호체결 시스템의 문제점인 취약한 구조적 안정성으로 인한 낮은

반복성을 개선하는 것에 목표를 두었으며, 선형 구조물의 도입과

관련하여 체결 현상이 효과적으로 발생하기 위한 구조물 사이의

간격비와 패턴의 크기에 대한 기하학적 분석 및 재료의 탄성

계수에 의한 접착 성능의 차이를 관측하였다. 이를 통해 얻어진

최적화된 구조물의 형상을 기반으로 그 구조적 우수성을 확인하기

위한 반복성 실험 및 분석이 진행되었다. 체결된 구조물에서

발생하는 접착력의 크기는 접촉면에서의 힘의 평형을 통해 설명할

수 있는데, 종횡비가 낮은 선형 구조물의 변형을 고려하기 위해

단순 보 이론 대신 티모센코 (Timoshenko)보 이론을

도입하였으며, 또한 접촉면에 존재하는 나노스케일의 표면거칠기에

의한 영향을 고려하였다. 이와 같은 분석을 바탕으로 본 논문에서는

기존의 방법보다 더 정확하게 선형 구조물의 체결 현상 및 접착력

실험 결과를 설명할 수 있는 이론을 수립하였다.

주요어 : 자연모사, 가역적 상호체결시스템, 선형 구조물,

건식 접착, 반데르발스 힘

학 번 : 2012-22563