Temperature-Triggered Gelation of Aqueous Laponite Dispersions Containing a Cationic Poly(N-isopropyl acrylamide) Graft Copolymer

Abstract

In this work, temperature-triggered gelation of aqueous laponite dispersions containing a cationic poly(N-isopropylacrylamide) (PNIPAm) graft copolymer was investigated. The copolymer used was PDMA(+)(30)-g-(PNIPAm(210))(14) [Liu et al. Langmuir 2008, 24, 7099]. DMA(+) is quarternarized N,N-dimethylaminoethyl methacrylate. The presence of small concentrations of laponite enabled temperature-triggered gel formation to occur at low copolymer concentrations (e.g., 1 wt %). Dynamic rheological measurements of the gels showed that they had storage modulus values of up to 400 Pa when the total solid volume fraction (polymer and laponite) was only about 0.02. The storage modulus was dependent on both the temperature and the composition of the dispersion used for preparation. The key component that provided the temperature-triggered gels with their elasticity was found to be self-assembled nanocomposite (NC) sheets. These NC sheets spontaneously formed at room temperature upon addition of laponite to the copolymer solution. The NC sheets had lateral dimensions on the order of hundreds of micrometers and a thickness of a few micrometers. The NC sheets were present within the temperature-triggered gels and formed elastically effective chains. The NC sheets exhibited temperature-triggered contraction with a contraction onset temperature of 27 degrees C. A conceptual model is proposed to qualitatively explain the relationship between gel elasticity and dispersion composition.

Thermoresponsive surfaces prepared using adsorption of a cationic graft copolymer: A versatile method for triggered particle capture

“…x -g-ðPNIPAm n Þ y to dispersed laponite particles renders the dispersions thermoresponsive [2]. A strong attractive interaction between the copolymer and laponite surface was apparent from those studies.…”

“…The present study also draws upon our previous work [2] involving laponite dispersions containing PDMA þ x -g-ðPNIPAm n Þ y . Laponite is a synthetic smectite clay which forms structured gels in concentrated dispersions.…”

“…For the MI-PNIPAm copolymers electrostatic attraction between the cationic copolymer and anionic laponite layer probably contributes to adsorption. Related work involving self-assembled laponite/MI2-PNIPAm20k nanocomposite micro-sheets has shown strong indirect evidence [2,38], of electrostatic attraction between the components.…”

“…Cationic PNIPAm copolymers been prepared as random [4], block [5,6], star [7,8] and graft copolymers [1,2,[9][10][11]. They have been actively studied in the context of gene delivery [9,10,12] and temperature-sensitive flocculants [4].…”

“…x -g-ðPNIPAm n Þ y copolymers can be found by the observation of self-assembly of micrometer sized nanocomposite sheets (micro-sheets) in mixed dispersions [2]. Here, we take advantage of attractive copolymer/laponite interactions to construct thermally-responsive surfaces.…”