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Sc cng b mtTrong vt l hc, sc cng b mt (cn gi l nng lng b mt hay ng sut b mt, thng vit tt l hay hay T) l mt di lc xut hin b mt gia cht lng v cc cht kh, cht lng hay cht rn khc; c bn cht l chnh lch lc ht phn t khin cc phn t b mt ca cht lng th hin c tnh ca mt mng cht do ang chu lc ko cng. Cc phn t trong cht lng lun chu nh hng ca cc lc phn t t cc phn t xung quanh. Vi cc phn t nm gia cht lng, chng c bao quanh mt cch i xng bi cc phn t cht lng cng loi khc, nn lc tng cng c cn bng thnh 0. b mt, mt bn cc phn t b cc phn t cng loi tng tc vi lc khc bn kia do cc phn t khc loi. Lc tng cng c th ko phn t b mt vo bn trong cht lng, nh trng hp b mt git nc trong khng kh, hay y n ra pha ngc li, nh trng hp git nc bm vo thnh ng mao dn. y l hiu ng lm cho git nc trong khng kh c hnh cu, h tr thc vt vn chuyn nc t r ln n l thng qua h mch dn phloem bng hin tng mao dn, gip nhn nc b trn mt nc, gii thch trng thi cn bng ca nh tng (t nc t n ph nang trong phi) cng nh tc dng ty ra ca x phng ni ring hay hot tnh ni chung ca cht hot ha b mt, ... Sc cng b mt c nh ngha l lc cng trn mt n v chiu di ct ngang b mt. Trong h o lng quc t, sc cng b mt c o bng Newton trn mt (Nm-1). Cng c th nh ngha sc cng b mt l cng c hc thc hin khi lc cng lm cho din tch b mt thay i mt n v o din tch. Nh vy n cng l mt din tch ca nng lng; ngha ny mang li tn gi nng lng b mt cho i lng vt l ny. Nh vy, trong h o lng quc t, n v o sc cng b mt tng ng Jul trn mt vung. Cht hot ng b mt (ting Anh: Surfactant, Surface active agent) l mt cht lm t c tc dng lm gim sc cng b mt ca mt cht lng. L cht m phn t ca n phn cc: mt u a nc v mt ui k nc.

c imCht hot ng b mt c dng gim sc cng b mt ca mt cht lng bng cch lm gim sc cng b mt ti b mt tip xc (interface)ca hai cht lng. Nu c nhiu hn hai cht lng khng ha tan th cht hot ha b mt lm tng din tch tip xc gia hai cht lng . Khi ha cht hot ha b mt vo trong mt cht lng th cc phn t ca cht hot ha b mt c xu hng to m (micelle, c dch l mixen), nng m ti cc phn t bt u to m c gi l nng to m ti hn. Nu cht lng l nc th cc phn t s chm ui k nc li vi nhau v quay u a nc ra to nn nhng hnh dng khc nhau nh hnh cu (0 chiu), hnh tr (1 chiu), mng (2 chiu). Tnh a, k nc ca mt cht hot ha b mt c c trng bi mt thng s l cn bng a k nc (ting Anh: Hydrophilic Lipophilic Balance-HLB),

gi tr ny c th t 0 n 40. HLB cng cao th ha cht cng d ha tan trong nc, HLB cng thp th ha cht cng d ha tan trong cc dung mi khng phn cc nh du. LAS :CH3-(CH2)n-C6H4)SO3H Lauryl aryl sulfonic y l cht hot ng b mt mnh, l phn a nc. N l hot cht chnh trong cc loi du gi . Gi rt r, t gy kch ng da, ty ra tt ---> c dng

Phn loiTy theo tnh cht m cht hot ha b mt c phn theo cc loi khc nhau. Nu xem theo tnh cht in ca u phn cc ca phn t cht hot ha b mt th c th phn chng thnh cc loi sau:

Cht hot ha ion: khi b phn cc th u phn cc b ion ha. o Cht hot ha dng: khi b phn cc th u phn cc mang in dng, v d: Cetyl trimtylamni brmua (CTAB). Cetyl trimetylammonium bromua (CTAB) Cetyl pyridinium clorua (CPC) Polyethoxylated tallow amin (POEA) Benzalkonium clorua (BAC) Benzethonium clorua (BZT) o Cht hot ha m: khi b phn cc th u phn cc mang in m Natri dodecyl sulfat (SDS), amoni lauryl sulfat, v cc mui ankyl sulfat khc Natri laureth sulfat, hay natri lauryl ete sulfat (SLES) Ankyl benzen sulfonat X phng v cc mui ca axit bo Cht hot ha phi ion: u phn cc khng b ion ha, v d: Ankyl poly(tylen xt). o Ankyl poly(etylen oxit) o Copolymers ca poly(etylen oxit) v poly(propylen oxit) (trong thng mi gi l cc Poloxamer hay Poloxamin) o Ankyl polyglucozit, bao gm: o Octyl glucozit Decyl maltosit o Cc ru bo Ru cetyl Ru oleyl o Cocamit MEA, cocamit DEA Cht hot ha lng cc: khi b phn cc th u phn cc c th mang in m hoc mang in dng ty vo pH ca dung mi, v d: Dodecyl imtylamin xt.o

Dodecyl betain Dodecyl dimetylamin xt Cocamidopropyl betain Coco ampho glycinat

ng dng:Cht hot ha b mt ng dng rt nhiu trong i sng hng ngy. ng dng ph bin nht l bt git, sn, nhum ... Ngoi ra nhng ng dng trong cc lnh vc khc nh

Trong cng nghip dt nhum: Cht lm mm cho vi si, cht tr nhum Trong cng nghip thc phm: Cht nh ha cho bnh ko, b sa v hp Trong cng nghip m phm: Cht ty ra, nh ha, cht to bt Trong ngnh in: Cht tr ngm v phn tn mc in Trong nng nghip: Cht gia cng thuc bo v thc vt, Trong xy dng: Dng nh ha nha ng, tng cng ng rn ca b tng Trong du kh: Cht nh ha dung dch khoan Trong cng nghip khong sn: Lm thuc tuyn ni, cht nh ha, cht to bt lm giu khong sn

Cc cht hot ng b mt truyn thng nh LAS, LES dng trong lnh vc ty ra l cc anionic surfactants, chng i km vi tnh cht to bt do ngi hay gi l cht to bt. Trong lnh vc hot ng b mt ngi ta thng gi tn theo cng dng vd. defoamer - cht ph bt, OW emulsifier - cht nh ho du trong nc, WO emulsifier - cht nh ho nc trong du, wetting agents (hoc penetrating agents) - cht thm t, ... Bn nn lm quen vi cc ethoxylates , chng l cc nonionic surfactants vd, nonyl ethoxylate, octyl ethoxylate, linear alkyl ethoxylate, PEO, polysorbate, ... ty theo mc ethoxylation (bao nhieu mol ethylene oxide cho 1 mol surfactant) ta s c h cht vi di ca dy polyether khc nhau => tnh HLB s c tr s t 1 n 20. HLB : 1-3 ph bt HLB : 4-9 nh nc trong du HLB : 9-11 wetting agents HLB : 11-15 nh du trong nc HLB > 15 cht khuch tn,