Ray Drumright

Polylactic acid is proving to be a viable alternative to petrochemical-based plastics for many applications. It is produced from renewable resources and is biodegradable, decomposing to give H2O, CO2, and humus, the black material in soil. In addition, it has unique physical properties that make it useful in diverse applications including paper coating, fibers, films, and packaging (see Figure).

A novel procedure for the preparation of superhydrophilic surfaces is described. The method employs fabricating the surface from a mixture of silica nanoparticles (NPs) and polymers containing reactive trimethoxysilyl (TMOS) groups. Suitable polymers include quaternized poly(2-(dimethylamino)ethyl methacrylate) (PQDMAEMA) and poly(3-(trimethoxysilyl)propyl methacrylate) (PTMOSPMA). Condensation of the TMOS groups in a deposited film occurs under mild conditions and results in formation of a cross-linked polymer-SiO(2) nanocomposite coating covalently anchored onto a glass substrate. When silica nanoparticles, containing micrometer-sized agglomerates, are introduced into the film, a hierarchical micro/nanostructure within the coating is built up. Superhydrophilic behavior is achieved with a high weight ratio of fumed silica NPs or polymer/fumed silica NP bilayer coatings. The superhydrophilic surfaces have high stability and antifogging behavior and display easy cleaning characteristics. Furthermore, the superhydrophilic nanocomposite coatings containing PQDMAEMA exhibit antimicrobial properties against E. coli due to the presence of quaternary ammonium groups.

In this study, the influence of an amino silane (3-(2-aminoethylamino)-propyldimethoxymethylsilane, AEAPS) on the interfacial structure and adhesion of butyl acrylate/methyl methacrylate copolymers (BAMMAs) to silica was investigated by sum frequency generation vibrational spectroscopy (SFG). Small amounts of methacrylic acid, MAA, were included in the BAMMA polymerizations to assess the impact of carboxylic acid functionality on the glass interface. SFG was used to probe the O-H and C═O groups of incorporated MAA, ester C═O groups of BAMMA, and CH groups from all species at the silica interfaces. The addition of AEAPS resulted in a significant change in the molecular structure of the polymer at the buried interface with silica due to specific interactions between the BAMMA polymers and silane. SFG results were consistent with the formation of ionic bonds between the primary and secondary amines of the AEAPS tail group and the MAA component of the polymer, as evidenced by the loss of the MAA O-H and C═O signals at the interface. It is extensively reported in the literature that methoxy head groups of an amino silane chemically bind to the silanols of glass, leaving the amine groups available to react with various chemical functionalities. Our results are consistent with this scenario and support an adhesion promotion mechanism of amino silane with various aspects: (1) the ionic bond formation between the tail amine group and acid functionality on BAMMA, (2) the chemical coupling between the silane head group and glass, (3) migration of more ester C═O groups to the interface with order, and (4) disordering or reduced levels of CH groups at the interface. These results are important for better understanding of the mechanisms and effect of amino silanes on the adhesion between acrylate polymers and glass substrates in a variety of applications.