Resumen de Smart controlled release membranes
During these centuries many studies were focused around the smart materials as promising way to boost and arise the performances of devices used in our daily life. As matter of interest, these polymers are being used in application like drug delivery, diagnostics, biotechnology, sensors, actuators and optical systems, as well as coatings, textiles and consumers goods. Scientists are creating system that could be more and more versatile and “smart”, depending on the conditions of the environments in which they are placed. The aim of this PhD project is to improve, the performance of the Air Care devices for small environments and cars, produced by Procter & Gamble company. In the specific, these are passive devices that work in a continuous manner evaporating fragrances from a porous membrane. This membrane represents the core of the Febreze product, and it allows the diffusion of the volatile materials with poor selectivity, while avoiding leakage of the liquid mixture with higher fragrance delivery rate per unit area. However, there are several possibilities of improving the performances of this membrane. For instance, in conditions of prolonged higher temperature, like in a hot parked car or household condition, too much fragrance can evaporate, affecting the longevity of scent experience to the consumer; another problem lies in the lack of control on the rate at which the top notes (more volatile part of the perfume) and the bottom notes (less volatile part of the perfume) evaporate from the membrane, which gives rise to an altered perception of the perfume, since the top notes come out much faster than the bottom ones. To get a better perfume spectrum balance, enabling the perfume to be delivered to the consumer according to the desired design, it would be preferred a membrane that could be tuned to set the rate of evaporation, depending on the volatility of the perfume components. A possible solution to some of these problems could lie in membrane coating with new and properly functionalized polymers, which could act as a selective “gate”, allowing or preventing the release of the volatile material under certain stimuli. As a matter of fact, the reversible changes of polarity and conformation imparted to a photochromic polymer system by photoirradiation can be applied to controlling mass transfer through membranes. For instance, it has been reported that azo-benzene based systems can successfully act as light-triggered membrane. At a molecular level, E-Z isomerization leads to a substantial change in geometric conformation and size. On the other hand, it is also known that the interaction of some polymer groups with the dipole of Z azobenzene form can lead to a change in the wettability and swelling degree of a membrane, thus modifying its permeability to low molar mass compounds. From the literature is well known that azobenzenes are very receptive to inclusion in different types of materials. This brilliant property of azobenzenes makes them useful in the preparation of different photoresponsive membranes. Moreover, the wavelength which induces the opening of the membrane, and subsequent release, could be adjusted by properly design the structure of the azo-bearing moiety. Darkness and/or temperature increase would drive the azobenzene units back to the more stable E configuration, thus inhibiting release. Moreover, since the so functionalized polymer is more polar when in its Z form, the “open” membrane would favour the release of hydrophilic fragrances over the hydrophobic ones, thus contributing to some flattening of the top and bottom notes. In conclusion, the objective of this PhD project is to improve the performance of Air Care devices developing a membrane that can release the perfume raw materials charged inside the reservoir without being extremely affected by temperature fluctuations of the external environment, thus, being significantly less temperature sensitive than the current membrane used in nowadays products. In order to do this the main membrane will be coated with a polymer modified with novel azobenzene moieties. This system could be triggered by light to act as an intelligent gate for the perfume diffusion, improving both selectivity and releasing control of the perfume raw materials in the home/car environment. In addition, by a proper design of the functionalizing unit, temperature could act as an additional external stimulus, able to conveniently trigger (i.e. reduce) membrane permeability through thermal back-isomerization.
