Phase transition in swollen gels. 21. Effect of acrylamide quaternary salts with various alkyl lengths on the collapse, mechanical, and SAXS behavior of poly(acrylamide) networks

Abstract

A series of ionic networks were prepared by copolymerization of acrylamide, methylenebis-(acrylamide), and A/-[2-(alkyldimethylammonio)ethyl]acrylamide with Cl, C4, C6, C8, C12, and C16 straight-chain alkyls (mole fraction of the last comonomer xi = 0-0.15). Small-angle X-ray scattering, swelling, and mechanical behavior of the networks were investigated in water-ethanol mixtures. For the gels with C1-C8 alkyls collapse was found; both the volume jump and the critical ethanol concentration at which the transition takes place, ec, increase with increasing content of the ionic component, xj.Increasing the alkyl length stabilizes the expanded state of the gel and increases the ec values, probably due to preferential sorption of ethanol by hydrophobic regions. Different swelling behavior was found for gels with C12 and C16 alkyls, where mostly a decrease in swelling in water at low ethanol concentrations was observed with increasing xi. This is caused by a distinct amphiphilic character of salts with the two longest alkyls; in networks with the C16 alkyl formation of micelles was proved by SAXS. Mechanical behavior of the networks is predominantly determined by the degree of swelling; a jumpwise change in the gel volume is accompanied by a similar change in the equilibrium modulus. amide)14 and polyCZV-isopropylacrylamide)4'15 hydrogels.

Phase transition in swollen gels

“…Usually 10 values of λ and f were determined. The shear modulus G was determined from the equation [7,8] where S 0 is the initial cross-section of the specimen. Swelling and mechanical experiments were carried out with samples immediately after preparation at room temperature (modulus G 1 , Table 1) and with the samples swollen to equilibrium in water at various temperatures in the range 15−90 °C or in aqueous NaCl solutions (modulus G) at 23 °C.…”

“…As positively charged comonomer (S), (2-acrylamidoethyl)trimethylammonium chloride was used which was synthesized as shown previously [7].…”

“…Swelling proceeded at achosen temperature (T) for four days or in aqueous NaCl solutions for one month, after which the inverse swelling ratio X relative to the state of network formation was determined from [7,8] where D* and D, respectively, are the sample diameters after preparation and swelling at various temperatures or in aqueous solutions, respectively, and V* and V are the corresponding swelling volumes. The diameters were measured with an Abbe comparator (accuracy ≈ 0.002 mm).…”

Compressive moduli and network parameters of N‐isopropylacrylamide hydrogels copolymerized by monoesters of itaconic acid and crosslinked with tetraallylammonium bromide

“…Ilavsky et al . reported that with increasing length of alkyl chains at a constant mole fraction of hydrophobically modified quarternary salts of acrylamide, the value of the swelling ratio decreased due to the increasing strength of the hydrophobic interactions.…”

“…reported that with increasing length of alkyl chains at a constant mole fraction of hydrophobically modified quarternary salts of acrylamide, the value of the swelling ratio decreased due to the increasing strength of the hydrophobic interactions. However, they observed that for the quaternary salt containing C 16 chains the swelling degree is independent of the comonomer mole fraction, and they concluded that the hydrophobic side chains with C 16 alkyl groups could form micelle‐like aggregates in the network . In our study, the Q rv values of S20 and S21 changed slightly with increasing concentration of mCeI (from 5.00 to 10.00 mol %) in the feed, but their swelling degrees were higher than that of the PNIPAAm hydrogels containing C 8 alkyl groups (Table ).…”