In the current context of sustainability, there is a growing interest in developing novel functional materials based on sustainable bioresources. Cellulose is one of the principal constituents of wood and plants and one of the most abundant resources on earth. In nature, the linear chains of this biopolymer are associated by hydrogen bonding to form a semicrystalline structure where highly ordered regions (the crystallites) are distributed among disordered domains (the amorphous phase). These crystallites are nanometer-sized and can be easily recovered by sulfuric acid treatment, combined with sonication. With this treatment, the amorphous regions of cellulose are hydrolysed and rod-like cellulose nanowhiskers (CNW) bearing anionic sulfate ester groups at their surface are produced. When they are dispersed in water, the cellulose nanowhiskers do not flocculate because of the electrostatic repulsions resulting from the negative surface charges, and the suspension is stable for several months. These suspensions have interesting characteristics since they are birefringent and can self-organize into stable chiral nematic phases when a critical concentration is reached (typical of liquid crystals). Because of their high specific strength, modulus and aspect ratio, the CNW can significantly improve the mechanical performances of polymers, at low loading levels, offering opportunities for new high value-added nanocomposite materials. But to achieve properties improvement, a good interfacial adhesion must be obtained and the CNW must be homogeneously dispersed in the polymeric matrix, which is non-trivial. Because of their high surface area and hydrophilic nature, the CNW cannot be easily dispersed in mediums of low polarity, rendering it difficult to efficiently reinforce most of the classical polymer matrices. The dispersability of the CNW in such medium can however be improved by surface functionalization: chemical functions can be grafted at the surface of the CNW to decrease the interfacial energy and increase their interaction with molecules of low-polarity (physical or chemical interactions).
In this context, we envisage developing novel nanocomposite materials through the controlled functionalization and self-assembling of CNW. An original method based on prior modification of CNW with vinyl esters followed by ATRP polymerization will be investigated. Material applications will be explored at the later stage of the PhD thesis. The grafting polymerization should lead to a range of new materials, such as cellulose surfactants, cellulose hydrogels, cellulose surpamolecular nanomaterials etc.
The successful candidate will have a Master degree in polymer chemistry or related fields. We expect a highly motivated, open-minded and flexible person with a strong interest in polymer chemistry and a fluent proficiency in English (TOEFL, IELTS or TOEIC are required). The thesis will be co-supervised by Dr Sèbe (University of Bordeaux - France) and Dr. Wang (University of Waterloo – Canada). The position is available immediately and is limited to 4 years.
To apply, please send a letter of motivation, CV and names and contacts of two references to:
Dr Gilles SEBE
Laboratoire de Chimie des Polymères Organiques (LCPO)
IPB/ENSCBP, 16 Avenue Pey Berland, 33607 PESSAC cedex, FRANCE
Tel: +33 (0)5 40 00 64 11
Fax: +33 (0)5 40 00 84 87
Laboratoire de Chimie des Polymères Organiques (LCPO), Université Bordeaux 1, France
Laboratory of Supramolecular Functional Nanomaterials, University of Waterloo, Canada