Flocculation and Aggregation Behavior of Doubly Responsive Microgel

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1 Vol. 66, , ACTA CHIMICA SINICA No. 4, a,b a a a *,a ( a ) ( b ) (N- -co- ), NMR, DLS. 25 ph 7 Zeta 18 mv,,. NaCl 0.2 mol/l,,.,, Zeta. 0.2 mol/l NaCl, 41 Zeta 12.4 mv,., Zeta,, (CFT). CFT,. N- ; ; ; Flocculation and Aggregation Behavior of Doubly Responsive Microgel LIU, Wei-Jun a,b ZHOU, Yuan a CHEN, Hou-Yang a HUANG, Yong-Min a LIU, Hong-Lai*,a ( a Key Laboratory for Advanced Material of Education Ministry, Department of Chemistry, East China University of Science and Technology, Shanghai ) ( b Department of Chemical Engineering, Shanghai Institute of Technology, Shanghai ) Abstract Poly(N-isopropylacrylamide-co-methacrylic acid) microgel was prepared by the precipitation polymerization method. NMR and TEM were used to analyze microstructure and morphology of the microgel. The stability and zeta potential of the microgel were investigated as a function of electrolyte concentration by dynamic light scattering. Zeta potential was 18 mv in ph 7 solution at 25, which decreased gradually with increasing ionic strength and reached an equilibrium value at 0.2 mol/l NaCl concentration, indicating that the surface charge of the microgel had been screened out. Increasing in NaCl concentration caused mainly the microgel particles to shrink. For the microgel in certain electrolyte solution, the heating induced the particles to deswell. As a result, the surface charge density became greater gradually, resulting in the increase of zeta potential. For microgel in 0.2 mol/l NaCl solution, the zeta potential was 12.4 mv at 41, playing an important role in stabilizing the microgel. The potential of the microgel at higher ionic strength displayed an abrupt transition of trending to zero as increasing the temperature, and the relevant temperature was correspondent with the critical flocculation temperature (CFT). The CFT of the microgel was shifted to lower temperature with the increase of NaCl concentration. At a certain salt concentration, the aggregation rate of the particles at a higher temperature was faster than that at a lower temperature. Keywords N-isopropylacrylamide; microgel; temperature sensitivity; stability * hlliu@ecust.edu.cn Received April 21, 2007; revised October 23, 2007; accepted November 3, (Nos , , ) (No. P1501).

2 450 Vol. 66, 2008, ph,. [1,2] [3.4] [5,6] [7 9]. 1 nm 1 µm., [10] 50 nm 5 µm,., (N- ). (N- ),, (VPTT), VPTT 32 35,, [11]. N-,. VPTT [12 14]. ph (MAA) N- (NIPAM), ph (N- -co- ) [15 17], MAA ph KCl VPTT., (N- ) MAA P(NIPAM-MAA), MAA, ph Zeta [18].,, ;,,. [18],, ph P(NIPAM-MAA). [15 17] ph, (DLS) P(NIPAM-MAA), Zeta,, (MAA, ), N- (NIPAM, ), N,N- (MBA, Fluka ), (APS, ), (SDS, ), (Na 2 HPO 4, ), (C 6 H 8 O 7, ), (NaCl, ). Zetasizer Nano S (DLS, Malvern), DRX500 (Burker), PHS-3C ph ( ), JEOL-1200EX ( ) 1.2 P(NIPAM-MAA). 1.9 g NIPAM 0.05 g MBA 250 ml, 100 ml, N 2, 0.1 g MAA 0.1 g SDS, SDS N 2 30 min. 70, 5 ml 0.1 g APS, 5 h r/min 45 min,, 1 h, 5 d,, P(NIPAM-MAA). ( ) 0.1% (w) , DLS, 173, 633 nm, DTS v4.0, 25, min,. D v /D n, D v, D n , 0.2 mol/l 0.1 mol/l, ph mol/l, NaCl, w 0.03%, DLS 25, Zeta.,. 10 min, 3,., Zeta. 0.4 mol/l, DLS, 36, 40.,, 5 min, 30 min 10 min, 2.5 h NMR DRX500 MAA, PNIPAM P(NIPAM-MAA), 1 H NMR 1. c δ 1.7, 2.1 δ 3.85

3 No , 25 (D z ) (25 D v, D n ),. (D v /D n ) 1.19,, H NMR : (a) MAA (DMSO-d 6 ), (b) PNIPAM (D 2 O), (c) P(NIPAM-MAA) (D 2 O) Figure 1 1 H NMR spectra of samples: (a) MAA (DMSO-d 6 ), (b) PNIPAM (D 2 O), (c) P(NIPAM-MAA) microgel (D 2 O) PNIPAM CHCH 2 NHCH ; δ 3.26 δ 4.92 H 2 O ; δ 1.1 CH 3, MAA, b. b, c a, δ 5.65, 6.03,. a δ 2.57, 3.4 DMSO-d 6 [19]. 2.2 TEM 2%,, 24 h [20], TEM 2. 2, P(NIPAM- MAA),, 100 nm. DLS 25, , 50 Figure 3 Size distribution of microgel particles at 25 and 50 3,, ,,,,,,,.,,,,,. 2.3 Zeta 4 25.,, 1.0 mol/l,,. (PDI), 1.0 mol/l,. 5, 5, 2 P(NIPAM-MAA) TEM Figure 2 TEM photograph of P(NIPAM-MAA) microgel 1 25, 50 Table 1 Various average s and polydispersity of microgel particles at 25 and 50 Temperature/ Z-average (D z /nm) Volume average (D v /nm) Number average (D n /nm) Polydispersity (D v /D n ) , Zeta,. van der Waals (V A ) [21], V A,., 0.2 mol/l,,,, mol/l. 5, 0.2 mol/l,.

4 452 Vol. 66, NaCl Figure 4 Diameter of microgel at various NaCl concentrations 6 NaCl Figure 6 Diameter of microgel at various NaCl concentrations as a function of temperature 5 NaCl Zeta Figure 5 Zeta potential of microgel at various NaCl concentrations.,, [22,23]., NaCl Cl, [24].,, (CCC). 2.4 Zeta 6.,.,,,, (CFT) [25,26].,, van der Waals,.,.,, [21,27], 7., Zeta, 0.2 mol/l 7 NaCl Zeta Figure 7 Zeta potential of microgel at various NaCl concentrations as a function of temperature, Zeta 12.4 mv,. 0.4 mol/l, Zeta,,, V A,. Hamaker,.,,,, Hamaker, V A [28 30]. Zeta. 0.8 mol/l CFT 0.4 mol/l, CFT, 0.8 mol/l 0.4 mol/l nm,,,. 2.5,

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