Preparation And Property Of Smart Composite Materials Based On Spherical Polyelectrolyte Brushes

The smart composite materials have been widely applied in many fields, such as nanoreactor, drug-controlled releasing, sensor and biological recognition, which have attracted many interests in the material fields. In this work, we firstly prepared dual-responsive spherical polyelectrolyte brushes (SPBs) and investigated the effect of charges distribution in the shells, structure and composite of comonomers on the temperature and pH sensitivity. Secondly, taken SPBs as carries, we in situ synthesized the water-soluble quantum dots (QDs) in its shells that obtained organic-inorganic hybrid fluorescence nanoparticles. We discussed the influence of reaction condition on its optical performance and the pH sensitivity of fluorescence nanoparticles. Finally, using SPBs as multi-functional crosslinkers, we in situ polymerized polymer chains from its shells and formed 3D-network hydrogel. We investigated the mechanical properties, swelling ability and stimuli response of hydrogels. The main results are listed as follows:1. The N-isopropylacrylamide (NIPAM) and N,N-diethylacrylamide (DEA) were polymerized with acrylic acid respectively that were grafted from polystyrene nanoparticles through photoemulsion polymerization method. The obtained P(NIPAM-AA) and P(AA-DEA) exhibited temperature and pH sensitivity. Due to the reactivity difference between comonomers, NIPAM>AA>DEA, the PAA exhibited uneven distribution in the shells of SPBs, which led to different stimuli-response of two kinds of SPBs. Increasing the content of AA from 0.025% to 5% (relative to mole of NIPAM/DEA), the diameter of P(NIPAM-AA) was increasing with AA due to the electrostatic repulsion between polymer chains. The diameter of P(AA-DEA) was increasing at low ionic strength and then decreased at high level. While the diameter of P(NIPAM-AA) largely decreased with ionic strength because of the salt screening effect. The range of low critical solution temperature (LCST) was enlarged with AA content. Due to the uneven distribution of AA in the shells, the P(NIPAM-AA) and P(AA-DEA) displayed staged shell-shrinkage at certain condition. Compared with the LCST and shrinkage ratio of P(AA-DEA), the LCST of P(NIPAM-AA) was higher and shrinkage ratio was smaller than P(AA-DEA).2. Using the SPBs with polystyrene core and poly(acrylic acid) (PAA) shells as nanoreactor, it could in situ synthesize the water-soluable quantum dots (QDs), such as CdS, ZnS and CdTe in the PAA shells. The prepared SPBs@QDs showed strong fluorescence which from green to red. The TEM photoes proved that the QDs were uniformly distributed in the shells. The SPBs@QDs was mono-dispersed in the solution without aggregation. By adjusting the experimental conditions, such as the content of SPBs, pH values, feed ratio of reactant, the size and fluorescence color of SPBs@QDs could be effectively controlled. The SPBs@QDs were responsive to pH values. The shrinkage of shells in the acid conditions led to fluorescence quenching of packed QDs. As the shells were swelling in the basic condition, the fluorescence could be recovered again. The SPBs@QDs displayed high stability, which could be stored for a long time in the dark without aggregation and precipitation. In acid and basic condition, the nanoparticles showed anti-photocorrosion properties in the visible light.3. Using SPBs as multi-functional crosslinkers, the monomers were in situ polymerized from the shells of SPBs that formed 3D-network hydrogels. The SPBs were constituted of PS cores and poly(N,N-dimethylacrylamide) (PDMAA) shells. The network polymer chains were high entangled with PDMAA shells and formed amounts of strong hydrogen bongdings, which strengthened the network. Using AA as the monomer, the prepared PAA/SPBs hydrogels exhibited outstanding tensile and compressive properties. The fracture elongation reached 9000% and the toughness was as high as 8500J/m2. Moreover, the hydrogels had notch-insensitivity, self-healing property and ultrahigh absorbency. The elongation was as high as 8000% with notch present in the samples, which was independent with notch’s type and length. The cut surfaces could be heeled as the samples were broken. The mechanical properties of healed samples were almost same to the smaples without cuts. The swelling ratio could reach 3000. Using NIPAM and AA as commoners, the P(NIPAM-AA)/SPBs hydrogels could sustain high level deformations. The tensile property was temperature-responsive. The tensile modulus increased and fracture elongation decreased with temperature respectively. The volumes of hydrogels showed fast response to temperature and pH changes. High temperature and low pH values were enable hydrogels deswelling, while low temparture and high pH values promoted hydrogels absorbing water and swelling rapidly. By adjusting the temparture and pH values, the volumes of hydrogels could be reversibly controlled.