title: Surface interaction forces of cellulose nanocrystals grafted with thermoresponsive polymer brushes.
abstract: The colloidal stability and thermoresponsive behavior of poly(N-isopropylacrylamide) brushes grafted from cellulose nanocrystals (CNCs) of varying graft densities and molecular weights was investigated. Indication of the grafted polymer brushes was obtained after AFM imaging of CNCs adsorbed on silica. Also, aggregation of the nanoparticles carrying grafts of high degree of polymerization was observed. The responsiveness of grafted CNCs in aqueous dispersions and as an ultrathin film was evaluated by using light scattering, viscosimetry, and colloidal probe microscopy (CPM). Light transmittance measurements showed temperature-dependent aggregation originating from the different graft densities and molecular weights. The lower critical solution temperature (LCST) of grafted poly(NiPAAm) brushes was found to decrease with the ionic strength, as is the case for free poly(NiPAAm) in aqueous solution. Thermal responsive behavior of grafted CNCs in aqueous dispersions was observed by a sharp increase in dispersion viscosity as the temperature approached the LCST. CPM in liquid media for asymmetric systems consisting of ultrathin films of CNCs and a colloidal silica probe showed the distinctive effects of the grafted polymer brushes on interaction and adhesive forces. The origin of such forces was found to be mainly electrostatic and steric in the case of bare and grafted CNCs, respectively. A decrease in the onset of attractive and adhesion forces of grafted CNCs films were observed with the ionic strength of the aqueous solution. The decreased mobility of polymer brushes upon partial collapse and decreased availability of hydrogen bonding sites with higher electrolyte concentration were hypothesized as the main reasons for the less prominent polymer bridging between interacting surfaces.
authors.affiliation: Department of Forest Biomaterials, North Carolina State University, Campus Box 8005, Raleigh, North Carolina, USA.
authors.forename: Justin O
authors.initials: JO
authors.lastname: Zoppe
authors.forename: Monika
authors.initials: M
authors.lastname: Osterberg
authors.forename: Richard A
authors.initials: RA
authors.lastname: Venditti
authors.forename: Janne
authors.initials: J
authors.lastname: Laine
authors.forename: Orlando J
authors.initials: OJ
authors.lastname: Rojas
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins; D002482:Cellulose / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D011108:Polymers; C052970:poly-N-isopropylacrylamide; D012965:Sodium Chloride; D002482:Cellulose