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Tnh bn tp hp ca h keoBi:

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Khi nim tnh bn vng ca h phn tn

Tnh bn vng ca h phn tn l kh nng duy tr c trng thi phn tn khng itheo thi gian. S bn vng ca cc h phn tn ch c tnh cch tng i, nu h tnti trong mt thi gian lu th gi l bn, cn trong mt thi gian ngn l khng bn.

Tinh bn vng ca h phn tn c chia lm 2 loi: tnh bn tp hp v tnh bn nghc. Hai yu t ny lin quan mt thit vi nhau.

Tnh bn tp hp ca h keo

Kh nng gi c phn tn v c trng ring ca cc ht pha phn tn l thco v bn vng tp hp. Kh nng phn b u pha phn tn trong mi trng lthc o v bn vng ng hc. Mun h phn tn tn ti, cc ht ca pha phn tnphi c phn b u trong ton mi trng. Nhng trong h, cc ht lun lun chuynng Brown do c kh nng va chm vo nhau. S va chm ny to iu kin ccht tp hp thnh cc ht ln hn, v di nh hng ca trng trng s sa lng xungy bnh. C th ni s tp hp cc ht l nguyn nhn trc tip dn n s ph v bn ng hc ca h.

bn ng hc c kho st chng 3, sau y ta ch cp n bn tp hpi vi h keo.

* Cc h keo l h d th, khc vi cc dung dch phn t, gia pha phn tn v mitrng phn tn c b mt phn chia ln nn c nng lng b mt d ln, nn phnln l khng ng nht nhit ng v khng bn tp hp. Trong h keo lun c khuynhhng din ra nhng qu trnh kt hp cc tiu phn nh thnh nhng tiu phn ln lmcho tng b mt phn chia gia cc pha gim xung. V th vn tnh bn tp hp cah keo l mt trong nhng vn trung tm ca ha keo, cn s keo t l c ch quantrng nht ca vic chuyn trng thi, thay i tnh bn vng, thng gp tt c cc hkeo in hnh.

* Cc h keo thng c tnh bn tp hp rt khc nhau. Mt s h sng vi giy sau khichng to thnh, nhng nhiu h keo tn ti trong thi gian di. Tnh bn tp hp ph


1/9

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thuc nhiu vo thnh phn ca mi trng phn tn v c th thay i nhiu khi avo h nhng lng rt nh cc cht in phn l.

Tnh bn tp hp v keo t ca h keo k lng

Theo nh hng ca ph gia cht in phn n bn ca h keo c th chia thnh 2nhm: h keo a lng v h keo k lng.

- Vi h keo a lng (lyophylle sol) nh h protein/nc:

Tc dng tng h gia pha phn tn v mi trng phn tn lm cho entropi ca htng ln (S > 0) dn n G = H - T.S < 0, nng lng t do trong qu trnh hnhthnh h gim, nn chng t phn tn vo nhau v h bn vng v mt nhit ng hc.

- Cn h keo k lng (lyophob sol), l h c b mt ring ln, nng lng lin kt bntrong pha phn tn ln hn ng k so vi nng lng tng tc gia cc pha, v skhc bit khng c iu ha bi yu t entropi, nn i vi chng: G = H -T.S > 0. Do , s phn tn khng th t xy ra, m n din ra c l do cng bnngoi hoc nh cc qu trnh khc (v d qu trnh ha hc). Ni cch khc, y l mth thng khng bn vng nhit ng v cc ht pha phn tn lun c khuynh hng linkt li vi nhau gim b mt phn cch (lm gim nng lng t do b mt).

Tnh khng n nh ca cc h keo k lng th hin do 2 hin tng: ti kt tinh v keot.

- S ht gim i do kt qu ca s ti kt tinh xy ra trong ton h. Ta bit cc ht nhc p sut hi v ha tan ln hn so vi ht ln, do xu hng cc ht ln th lndn ln, s ht gim xung. Sau mt thi gian khi cc ht ln, h s mt bn salng. Nhng v cc pha phn tn thng c ha tan nh nn s ti kt tinh thngxy ra rt chm v trng hp ny t gp.

- Nhiu ht dnh kt li thnh tp hp ln hn (hp th) v dn n mt bn sa lng,gi l s keo t (coagulation). S keo t l hin tng ph bin i vi cc h keo trongmi trng phn tn lng v kh.

Trong trng hp cc h keo lng v kh do keo t m cc ht hon ton dnh chp lith c gi l s kt t (coalescence).

Cc yu t nh hng n tnh bn tp hp

Cc yu t c ngha quyt nh i vi tnh bn tp hp, l: nh hng ca nnglng tng tc gia cc micelle keo khi tip cn, nh hng ca hng ro hp ph


2/9

solvat ha bao quanh ht ngn cn s tip xc gia cc ht vi nhau, s hp ph cccht lm bn h keo.

nh hng ca nng lng tng tc gia cc micelle keo

Khi a 2 ht keo li gn nhau, c 2 lc i lp nhau ng thi xut hin.

- Lc ht phn t t l nghch vi khong cch x gia 2 ht keo. Tng ng vi lc htphn t c nng lng ht Q. Q= k

x3(6.1)

Trong k l hng s ph thuc vo bn cht ca h. Ta thy nng lng ht t l nghchvi ly tha ba khong cch gia hai ht.

- Lc y tnh in. Lc ny ch xut hin khong cch gn, khi lp khuch tn cacc ht micelle bt u ph nhau mt phn.

Lc y tnh in cng gim theo khong cch. Khi cc ht tin li gn th c s phnb li nhng ion cht in ly trong mi trng phn tn khu vc gia cc ht keo. Sphn b lm xut hin mt p sut ch chng li s tin gn cc ht . Do , lcy tnh in ph thuc vo khong cch theo mt hm s phc tp, n ph thuc voc 1 v ca h.

Tng ng vi lc y tnh in c nng lng P ph thuc vo khong cch theo mthm s m. P = c . ebx (6.2)

Trong , c v b l nhng hng s ph thuc vo bn cht ca h.

- Cc h thc (6.1),(6.2) cho thy lc ht, lc y u ph thuc vo khong cch

- t E = P - Q , gi tr ca E quyt nh th nng tng tc ca ht.

S ph thuc E vo khong cch c xc nh bng thc nghim.

Nu E > 0 : hai ht keo s y nhau.

E < 0 : hai ht keo s ht nhau.


3/9

th biu din s ph thuc ca th nng E vo khong cch x gia hai ht keo

th cho thy c mt gi tr x = xo ti E = Emax. Gi tr Emax gi l thm th nngca h keo.

nh hng ca s solvat ha

Cc h keo lng c th bn vng nh s solvat ha, trong trng hp cc phn t capha phn tn v ca mi trng phn tn c tng tc vi nhau, c lin kt hydro haylin kt ha hc vi nhau. Trn b mt ht s c mt lp solvat ha gm cc phn t cami trng phn tn. Cc h keo a lng mi c th c s solvat ha.

S c mt ca lp solvat ha lm cho cc ht khi va chm khng lin kt vi nhau. TheoDeryagin l do c p sut ch xut hin ti hai lp cht lng solvat ha trn b mtcc ht. p sut ch c to ra do s sai khc cu trc ca lp solvat b mt phn chiaso vi mi trng phn tn. p sut ny khng c bn cht tnh in.

nh hng ca cht lm bn

Cc lp phn t cht hot ng b mt c hp ph nh hng bo ha tng t nhmt cu to tinh th hai chiu c tnh cht lm bn cho h. Cc cht nh protit, x phngc kh nng to nhng lp nh vy.

Tnh cht c hc cu th ca cht lm bn c nh hng n s bn vng ca h keo.V d bn ca nh tng s tng ln, nu trn b mt phn cch pha c mt lp phnt cht lm bn c nht cu th cao hoc c bn vng c hc cao lm hng ro chc cu th ngn cn s dnh kt cc ht.

S bn vng do lp hp ph cht lm bn c th dn ti s bn vng vnh vin. V dbng cch to gel hay trng hp ha... lm cho lp cht lng gia cc bt kh tr thnhrn thu c cht do bt, b tng bt.


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iu kin h keo c bn

Trong chuyn ng Brown, cc ht keo mang nhng nng lng xc nh v c th vachm vo nhau ng vi mt xc sut no . iu kin h keo c bn l phi lmcho nng lng chuyn ng Brown lun lun nh hn thm th nng Emax ca h,mun th xc sut va chm vo cc ht keo phi nh.

Ni chung, mun cho h keo c bn vng, phi lm tng lc y tnh in, lm gimxc sut va chm hiu qu ca cc ht keo.Thng ngi ta s dng cc phng php:

- To cho b mt cc ht keo hp ph in tch (lm tng 1 v )

- Gi cho h keo c nng nh.

- To cho b mt ht keo hp ph cht bo v (cht hot ng b mt hoc mt s hpcht cao phn t nh geletin, polyvinil alcol . . .)

S keo t

Cc yu t gy keo t

S keo t l hin tng i lp vi vic to ra keo bn cho h phn tn. Hin tng nyxy ra khi cc ht dnh kt li vi nhau to thnh tp hp ln hn v dn n s binmt bn sa lng.

C nhiu nguyn nhn lm xy ra hin tng keo t nh: thi gian (s gi ca h keo),tc dng ca trng in t, tc dng c hc, un nng hay lm lnh, s c mt ca chtin ly. Mi loi tc dng u c mt c im ring, nhng c im chung cho chngl: ph hng ro nng lng v h thng gi bn, chuyn sang trng thi bn vng nhitng (gim nng lng t do ca h). S keo t xy ra trong h keo l cc ht trc tipdnh kt vi nhau khi chng va chm vo nhau, nhng khng phi bt c va chm nocng a n s dnh kt m ch c mt t l va chm nht nh l c hiu qu.

Tnh cht ca b mt ht c nh hng n s keo t. Khi thm mt lng nh cht hpph vo h, nhng tnh cht b mt thay i mnh v hiu qu ca cc va chm cngthay i. Khi hu ht cc va chm u dn n s dnh kt th ta gi l s keo t nhanh.Keo t chm l keo t m ch c mt phn trong s cc va chm dn ti s dnh kt.Kho st ng hc ca s keo t nhanh cho thy tc ca s keo t (hay s thay inng ht trong mt n v th tch v mt n v thi gian) ph thuc vo cc yu t:nng ht ban u, bn knh hot ng ca ht, h s khuch tn.

Trong phn ny chng ta ch yu kho st s keo t bng cht in ly, l s keo t c ngha l thuyt v thc t quan trng hn c.


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S keo t bng cht in ly

- Hu ht cc cht in ly u c kh nng gy keo t.

Kh nng keo t ca mt cht in ly c c trng bng ngng keo t , l nng ti thiu ca cht in ly cn keo t sol vi mt tc nht nh. i lng nythng c tnh theo mM (milimol/lit).

Qui tc Schulze- Hardy

* Ch c cc ion tch in tri du vi ht keo mi c kh nng keo t.

* Kh nng keo t ca cc ion cng ln (ngng keo t cng nh) nu ha tr ca chngcng cao; i vi cc ion c cng ha tr th kh nng keo t tng khi bn knh ion tng.V d: kh nng keo t ca Ca2+ ln hn ca Na+

kh nng keo t ca Rb+ ln hn ca NH4+ ln hn ca K+

kh nng keo t ca I- ln hn ca Br- ln hn ca NO3- ln hn ca Cl-

Nhng ion hu c c kh nng keo t mnh hn nhiu so vi nhng ion v c c cngha tr bi v chng km phn cc v b hp ph mnh trn b mt ht keo.

- Deriagin () a ra phng trnh biu din s ph thuc ca ngng keo t v ha tr ca ion gy keo t nh sau: = C.

3(kT)5

A2.e6.z6(6.3)

Trong : ngng keo t l s mili ng lng gam cht in ly cho vo 1 lit dungdch keo c nng xc nh gy nn keo t c th quan st c;

C v A l cc hng s; e l in tch ca electron;

z l ha tr ca ion i; l hng s in mi ca cht lng.

- Trong s keo t nhanh, tc keo t t l thun vi bnh phng nng ht.

Vkt = k. 2 (6.4)

Theo Smolukopski, k l hng s vn tc keo t, ph thuc vo khuch tn D vkhong cch d gia tm 2 ht keo: k = 4.D.d

Thay D t phng trnh Einstein v d = 2r, ta tnh c k = 4R.T3.NA (m3.s-1) (6.5)


6/9

Ti thi im t = 0, nng ht ng u trong ton b th tch v bng o. Khi xy rakeo t, nng ht gim, nn i < o.

T phng trnh (7. ) ly tch phn v thc hin cc bin i, ta c 1i 1o

= k.t

1i =1 + o.k.t

o i =

o1 + k.t.o

(6.6 )

Trong i l nng ht ti thi im t, o l nng ht lc u

Ti thi im m nng ht cn bng phn na lc u, ng vi thi gian gi l thiim bn keo t, ta tnh c nng bn keo t l: =

o

1 + t(6.7)

Cc hin tng c bit trong qu trnh keo t bng cht in ly

Hin tng i du in.

Khi thm dn dn mt lng ion keo t c ha tr ln (Fe3+,Al3+,PO43-...) hoc nhngcht c kh nng hp ph c bit nh cc cht mu, cc alkaloid ...vo sol th lc usol vn bn vng sau sol keo t khong nng nht nh; nu tip tc tng lngion keo t th h keo li ln lt chuyn trng thi sol v keo t. Hin tng ny gi lhin tng i du in; c th gii thch nh sau:

Lc u, khi cha cho vo h cht in ly (C = 0), h c th in ng o. Khi thm chtin ly vo h, do cation keo t c ha tr cao, n c hp th mnh vo ht nhn keolm trung ha bt anion quyt nh hiu th, do o gim.

- vng th I, gi tr ca gim nhng vn ln hn gi tr ti hn ( > - 30mV) v vyh keo c km bn hn lc u nhng vn cha b keo t.

- vng II, C1 C C2 , gi tr ca u nh hn gi tr ti hn, cc va chm u chiu qu, h b keo t. Trong vng ny lc C = C2 lng anion quyt nh hiu th btrung ha in hon ton vi cation b hp th, khi lp khuch tn cng trung hain tch. Lc C > C2 in tch cation hp ph vt in tch anion quyt nh hiuth, lc ny ht keo t m chuyn thnh dng.

- Trong vng III, C2< C C4 , do ht keo hp th thm cation nn tng vt gi trgii hn, s va chm hiu qu gim xung, v vy h keo li bn vng. ng vi gi trC = C3, b mt ht keo hp th bo ha cation keo t nn = max . Khi C > C3 , do bmt khng hp th c cation keo t na, nn cht in ly thm vo thnh cht in lytr, c tc dng lm cho lp kp nn li v gim ti tr s ti hn mi.

- T nng C5 > C4 tr i h li b keo t hon ton ( vng IV )


7/9

Hin tng keo t do tc ng ca hn hp cht in ly.

a. Hin tng kt hp: Hai cht in ly cng tc dng vi nhau (kt hp). Trong hnhp, kh nng keo t ca tng cht in ly khng thay i, khi thm lng cht ny thlng cht kia cng tng tng ng.

b. Hin tng cn tr: Hai cht in ly phn tc dng vi nhau. Nu mun keo t solphi thm cht in ly th hai nhiu hn so vi khi ch thm mt cht in ly.

c. Hin tng h tr: Hai cht in ly to iu kin keo t cho nhau, hay ni cch khclm tng kh nng keo t ca nhau. Trong trng hp ny, ta ch cn thm mt lngnh cht in ly th hai vo h.

Hin tng bo v

Cc h keo in hnh thng rt nhy cm i vi tc dng ca cht in ly nhng nutrc khi cho cht in ly keo t ngi ta thm vo h mt cht cao phn t th s hpph cht cao phn t ln b mt lm tng bn vng ca h keo. Khi h keo nyc th sy kh v sau c th phc hi trng thi keo khi ha tan tr vo dung mi c.Hin tng ny gi l hin tng bo v.

Nhng cht c kh nng bo v l cc protit, hydrocarbon, pectin... Cao su c th bo vh c mi trng phn tn khng phi l nc.Tuy nhin trong trng hp ny nhngcht lm kt ta cht bo v s ng thi gy s kt ta sol, d n khng c tc dng gring i vi sol.


8/9

S keo t d th v tng h

Trn thc t, ta thng gp nhng qu trnh trong cc ht ca h phn tn dnh vomt b mt khng cng loi vi chng, v c gi l s keo t d th. Hin tng nyrt quan trng trong k ngh thuc da, nhum, giy . .

Cc ht ca hai sol tch in ngc du c th gy s keo t ln nhau gi l s keo ttng h. Mun cho sol keo t hon ton phi ly t l gia hai sol nh th no choin tch ca cc ht hu nh trung ha ht.


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Tnh bn tp hp ca h keoKhi nim tnh bn vng ca h phn tnTnh bn tp hp ca h keoTnh bn tp hp v keo t ca h keo k lng

Cc yu t nh hng n tnh bn tp hpnh hng ca nng lng tng tc gia cc micelle keonh hng ca s solvat hanh hng ca cht lm bn

iu kin h keo c bnS keo tCc yu t gy keo tS keo t bng cht in lyQui tc Schulze- Hardy

Cc hin tng c bit trong qu trnh keo t bng cht in lyHin tng i du in.Hin tng keo t do tc ng ca hn hp cht in ly.Hin tng bo vS keo t d th v tng h

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