To reveal the structure and release properties of bentonite-alginate nanocomposites, bentonite of different amounts was incorporated into alginate by the sol–gel route. The structure of the composites was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis and related to the swelling property of the matrix and the release of imidacloprid. Bentonite was subject to exfoliation into nanoplatelets and combined into the polymeric network within alginate hydrogel, exhibiting profound effects on the structure features and release properties of the composites. Bentonite was of good compatibility with alginate due to the hydrogen bonding and the electrostatic attraction between them. The polymer chains were found to intercalate into the interlayer gallery of the clay. The high specific area of the nanoplatelets of bentonite benefited the intimate contact with alginate and reduced the permeability of the composites. However, in the composites with clay content of more than 10%, the polymer was insufficient to accommodate the silicate sheets completely. The aggregation of the platelets destroyed the structure integrity of the composites, facilitating the diffusion of the pesticide. The release of imidacloprid was greatly retarded by incorporating into bentonite-alginate composites and dominated by Fickian diffusion depending on the permeability of the matrix. The time taken for 50% of the active ingredient to be released, T 50, first increased and then decreased with increasing clay content in the composites, reaching a maximum around a weight percentage of 10%, at which the T 50 value for imidacloprid release was about 2.5 times that for the release from pure alginate formulation.

Thermodynamics and kinetics of pretilachlor adsorption on organobentonites modified with hexadecyltrimethyl ammonium chloride were investigated to reveal the structural effects of organobentonites on the interaction with pretilachlor and the diffusion of the herbicide and were related to the controlled release from organobentonites. The adsorption of pretilachlor was entropically driven by hydrophobic interaction. The entropy change dropped with increasing surfactant loading from 0.4 to 1.50 times the cation exchange capacity (CEC) of the bentonite used, corresponding to a decrease in the degree of freedom of pretilachlor molecules due to the enhanced order of surfactant in the interlayer. The kinetics of pretilachlor adsorption was well fitted to the pseudo-second-order model and related to the structural features of organobentonites. The enhanced packing density of the surfactant in the interlayer generally resulted in a reduction of the rate constant of the pretilachlor adsorption onto organobentonites. However, the stepwise increase in the basal spacing due to the surfactant arrangement transition, from lateral-monolayer to lateral-bilayer at a loading level of more than 0.8 × CEC, benefited the diffusion of pretilachlor and diminished the influence of the increase in surfactant packing density. The release of pretilachlor from organobentonites was predominated by Fickian diffusion, which could be understood from the adsorption thermodynamics and kinetics. The time taken for the release of 50% of active ingredient was 16–23 times that for the control formulation and exhibited a linear increase with the relative value of the equilibrium constant to the rate constant of pretilachlor adsorption.

For a better understanding on the interaction between polyethyleneimine (PEI) and proteins, spectroscopic studies including UV–vis absorption, resonance Rayleigh scattering, fluorescence, and circular dichroism were conducted to reveal the conformational change of rabbit muscle lactate dehydrogenase (rmLDH) and related to the bioactivity of the enzyme. Regardless of the electrostatic repulsion, PEI could bind on the surface of rmLDH, a basic protein, via hydrogen binding of the dense amine groups and hydrophobic interaction of methyl groups. The competitive binding by PEI led to a reduction of the binding efficiency of rmLDH toward β-nicotinamide adenine dinucleotide, the coenzyme, and sodium pyruvate, the substrate. However, the complex formation with PEI induced a less ordered conformation and an enhanced surface hydrophobicity of rmLDH, facilitating the turnover of the enzyme and generally resulting in an increased activity. PEI of higher molecular weight was more efficient to induce alteration in the conformation and catalytic activity of the enzyme.

The structure evolution of silk fibroin (SF) in the nanocomposite films with graphene oxide (GO) was investigated and related to the enzymatic degradability and release property. The interaction with GO was found to induce conformation transition of SF from random coil to β-sheet. However, the surface binding constrained the rearrangement of the silk chains, leading to a decrease of β-sheet when GO content was more than 1.0%. The crystal structure of SF played a key role in the degradation of GO/SF composites. The preferential degradation of the hydrophilic blocks resulted in a faster degradation of SF films with higher β-sheet content. The addition of GO to SF matrix led to a slower release and a reduction of the burst release of RhB, the model compound. The release profile was well fitted to the Rigter-Peppas equation, from which the characteristic constant decreased and the diffusional exponent increased with increasing GO content but quickly leveled off when GO content was more than 1.0%. Degradation of the composites had little influence on the characteristic constant of RhB release, however, led to an increased diffusional exponent, which was more evident for the composites with higher β-sheet content.