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Digital archive of theses discussed at the University of Pisa


Thesis etd-02242021-102830

Thesis type
Tesi di dottorato di ricerca
Thesis title
Self-assembling behaviors of amphiphilic polymers: From unimer micelles in solutions to nanostructured surfaces in thin films
Academic discipline
Course of study
tutor Prof. Galli, Giancarlo
supervisore Dott.ssa Martinelli, Elisa
  • amphiphilic polymers
  • DLS
  • LCST
  • multi.chain aggregates
  • SANS
  • SAXS
  • Self-assembly
  • thermoresposive polymers
  • unimer micelles
  • zwitterionic polymers
Graduation session start date
The PhD work was aimed to investigate novel types of amphiphilic synthetic polymers, where hydrophobic intramolecular interactions drive self-assembling into nanostructures in water solution and at the surface of thin solid films. In particular, attention was focused on the understanding of the morphology of self-assembled structures in relation to the nature of the hydrophobic component in the different polymers and to the variation of the temperature and concentration. To obtain a good control on the (co)polymerization the ARGET-ATRP and RAFT methods were used.
In this way, we succeeded in preparing (co)polymers featuring diverse chemical architectures as well as tailored and varied philic/phobic balances. Three major classes of amphiphilic polymers were newly developed: i) Random copolymers of polyethyleneglycol methyl ether methacrylate (PEGMA) as an hydrophilic and thermoresposive component with perfluorohexylethyl acrylate (FA) or polydimethylsiloxane methacrylate (SiMA) as an hydrophobic component. Triethyleneglycol methyl ether methacrylate (TRIGMA) was also used as an alternate comonomer in order to depress hydrophilicity of the respective copolymers. ii) Homopolymers of hydrophobic tetrafluorostyrene monomers modified by inserting an oligoethylene segment with varied chain lengths. iii) Random copolymers based on hydrophilic zwitterionic phosphorylcholine methacrylate (MPC) or sulfobetaine methacrylate (MSA) with 3-(trimethoxysilyl)propyl methacrylate (PTMSi) and copolymers of an hydrophobic FA with PTMSi.
Detailed characterization of the (co)polymers by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) measurements confirmed the formation of self-folded, intrachain nanostructures, or unimer micelles, for amphiphilic fluorinated copolymers of type i) in water solutions at room temperature. All polymers exhibited a reversible LCST-like behavior in water solutions, as identified by a transition temperature Tc that depended on the nature and composition of the amphiphilic polymers. The self-folded nanostructures clustered together into interchain aggregates above Tc, that quite reversibly collapsed back to unimer micelles on cooling below Tc. By contrast, all copolymers showed a conventional random coil conformation in organic solvents. A similar thermoresponsive behavior of intrachain nanostructures was observed with homopolymers of type ii), whose Tc was influenced by the overall hydrophobic/hydrophilic balance, as identified by the length of poliethylene glycol side chains. Fluorescent molecular probes were used to observe the self-assembly behavior of fluorinated amphiphilic copolymers. In particular, the single chain folding process was investigated through both a covalent functionalization and physical dispersion of two different hydrophobic dyes (2-cyano-2-[4-[vinyl(1-1’-biphenyl)-4’-yl]vinyljulolidine (JBCF) and coumarin 153 respectively) by fluorescence emission spectroscopy. The results of these preliminary analyses suggested the possibility of using the designed fluorinated copolymers as systems for controlled loading of hydrophobic molecules and possible release in response to a change in the embedding environments.
Random copolymers of type iii) were developed in which the zwitterion monomers MPC or MSA and hydrophobic FA were combined with functional PTMSi for tethering on glass substrates, thereby creating functional supported films incorporating nanostructuring additives. Experiments by static contact angle measurements, X-ray photoelectron spectroscopy, surface zeta potential and fluorescence spectroscopy analyses were applied to prove the effective anchoring of the polymeric films on the glass substrate before and after immersion in water. Then, antifouling potential of the films was demonstrated in biological assays against the adhesion of the yeast pathogen Candida albicans, chosen as a model fungal microorganism. The fluorinated copolymers were much more able to reduce fungal adhesion than did the zwitterionic MPC and MSA polymers.