7 research outputs found
Associations macromoléculaires en solution et aux interfaces : stimulation et ciblage par le pH et la température
We are investigating the assembling properties of responsive polymers in bulk and at interfaces. The assembling properties are tuned with temperature and pH by using complementary units. Associations are induced by a lower critical solution temperature (LCST) type phase separation taking place at a local scale. Introducing weak acid or base units in thermoassociative copolymers leads to pH-sensitive polymers. Two different random copolymers are obtained: one including weak acid units (Acrylic Acid (AA)), the other one including weak base comonomers (N,N - [(dimethylamino) propyl] methacrylamide (MADAP)). While all ionized copolymers remain soluble in water at all temperatures, their mixtures show a phase separation above a critical temperature due to the formation of a reversible inter-polyelectrolyte complex. When the responsive stickers are grafted on a poly(acrylamide) backbone, pH and temperature are still able to drive the association process at a local scale, giving rise to a sol/gel transition of semi-dilute solutions. The structure and the viscoelastic properties of these macromolecular assemblies are investigated by small angle neutron scattering and rheology. The environmental parameters (pH, temperature, ionic strength) and the addition of stickers with opposite charge can trigger specific association. In an original way, knowledge from associative properties in bulk is applied to interfaces to study adaptive surfaces. Specific interactions between polymer brushes and macromolecular solutions are characterized by ellipsometry and neutron reflectivity. We show that the adsorption of free grafts and comb copolymers on homopolymer brushes is controlled by environmental conditions (pH and temperature) and is completely reversible.Nous étudions les propriétés associatives de polymères stimulables en solution et aux interfaces. Les associations sont contrôlées par la température et le pH en utilisant des unités complémentaires. Les associations sont induites par une séparation de phase de type LCST. L'introduction de motifs ionisables dans ces chaînes de PNIPAM permet de rendre le polymère également sensible au pH. Deux séries de copolymères sont ainsi préparées : l'une comportant des motifs acides faibles dans la chaîne à LCST (unités d'Acide Acrylique (AA)), l'autre possédant des unités bases faibles ((N,N - methacrylamide de [(diméthyl amino) propyle] (MADAP). Alors que les polymères précurseurs PNIPAM-AA et PNIPAM-MADAP sous forme ionisée ne présentent pas individuellement de comportement thermo-associatif, leur mélange permet de générer une agrégation originale faisant intervenir une complexation électrostatique induite par chauffage. Le greffage de ces moteurs macromoléculaires sur un squelette hydrosoluble de poly(acrylamide) permet d'envisager la formation de gels réversibles en solution semi-diluée étudiée par DSC, rhéologie et diffusion de neutrons aux petits angles. Le choix des paramètres environnementaux (pH, température, force ionique) ainsi que l'addition de polymères précurseurs de charge opposée aux greffons permet de piloter l'association de manière très spécifique. De manière originale, les connaissances issues des propriétés associatives en solution sont appliquées aux interfaces pour rendre les surfaces adaptatives. Les interactions spécifiques entre des brosses de polymères et des solutions macromoléculaires sont caractérisées par ellipsométrie et par réflectivité de neutrons. Nous montrons que l'adsorption de polymères précurseurs et de copolymères en peigne sur des brosses d'homopolymère est contrôlée par les conditions environnementales (pH et température) et est complètement réversible
Associations macromoléculaires en solution et aux interfaces (stimulation et ciblage par le pH et la température)
Nous étudions les propriétés associatives de polymères stimulables en solution et aux interfaces. Les associations sont contrôlées par la température et le pH en utilisant des unités complémentaires. Les associations sont induites par une séparation de phase de type LCST. L introduction de motifs ionisables dans ces chaînes de PNIPAM permet de rendre le polymère également sensible au pH. Deux séries de copolymères sont ainsi préparées : l une comportant des motifs acides faibles dans la chaîne à LCST (unités d Acide Acrylique (AA)), l autre possédant des unités bases faibles ((N,N methacrylamide de [(diméthyl amino) propyle] (MADAP). Alors que les polymères précurseurs PNIPAM-AA et PNIPAM-MADAP sous forme ionisée ne présentent pas individuellement de comportement thermo-associatif, leur mélange permet de générer une agrégation originale faisant intervenir une complexation électrostatique induite par chauffage. Le greffage de ces moteurs macromoléculaires sur un squelette hydrosoluble de poly(acrylamide) permet d envisager la formation de gels réversibles en solution semi-diluée étudiée par DSC, rhéologie et diffusion de neutrons aux petits angles. Le choix des paramètres environnementaux (pH, température, force ionique) ainsi que l addition de polymères précurseurs de charge opposée aux greffons permet de piloter l association de manière très spécifique. De manière originale, les connaissances issues des propriétés associatives en solution sont appliquées aux interfaces pour rendre les surfaces adaptatives. Les interactions spécifiques entre des brosses de polymères et des solutions macromoléculaires sont caractérisées par ellipsométrie et par réflectivité de neutrons. Nous montrons que l adsorption de polymères précurseurs et de copolymères en peigne sur des brosses d homopolymère est contrôlée par les conditions environnementales (pH et température) et est complètement réversible.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
Synthesis and Characterization of Poly(acrylic acid) Brushes: "Grafting-Onto" Route
International audienceA guideline for the synthesis of poly(acrylic acid) brushes on planar silica surfaces by the grafting-onto approach is described. It is demonstrated that some thermal precautions must be taken to obtain extended brushes. It is also shown that neutron reflectivity is well suited for the characterization of each step of the synthesis, while it is (unfortunately) rarely used for that purpose. The steps are the following: first, the substrates are covered with a self-assembled monolayer of epoxy-terminated molecules; then, the poly(tert-butyl acrylate) brushes are built using preformed and end-functionalized chains; finally, the deprotection of the ester group is performed using a pyrolysis reaction to convert the poly(tert-butyl acrylate) brushes into poly(acrylic acid) brushes
Responsive Adsorption of N-Isopropylacrylamide Based Copolymers on Polymer Brushes
International audienceWe investigate the adsorption of pH-or temperature-responsive polymer systems by ellipsometry and neutron reflectivity. To this end, temperature-responsive poly (N-isopropylacrylamide) (PNIPAM) brushes and pH-responsive poly (acrylic acid) (PAA) brushes have been prepared using the "grafting onto" method to investigate the adsorption process of polymers and its reversibility under controlled environment. To that purpose, macromolecular brushes were designed with various chain lengths and a wide range of grafting density. Below the transition temperature (LCST), the characterization of PNIPAM brushes by neutron reflectivity shows that the swelling behavior of brushes is in good agreement with the scaling models before they collapse above the LCST. The reversible adsorption on PNIPAM brushes was carried out with linear copolymers of N-isopropylacrylamide and acrylic acid, P(NIPAM-co-AA). While these copolymers remain fully soluble in water over the whole range of temperature investigated, a quantitative adsorption driven by solvophobic interactions was shown to proceed only above the LCST of the brush and to be totally reversible upon cooling. Similarly, the pH-responsive adsorption driven by electrostatic interactions on PAA brushes was studied with copolymers of NIPAM and N,N-dimethylaminopropylmethacrylamide, P(NIPAM-co-MADAP). In this case, the adsorption of weak polycations was shown to increase with the ionization of the PAA brush with interactions mainly located in the upper part of the brush at pH 7 and more deeply adsorbed within the brush at pH 9
Large-Area Patterning of the Tackiness of a Nanocomposite Adhesive by Sintering of Nanoparticles under IR Radiation
We present a simple technique to
switch off the tack adhesion in
selected areas of a colloidal nanocomposite adhesive. It is made from
a blend of soft colloidal polymer particles and hard copolymer nanoparticles.
In regions that are exposed to IR radiation, the nanoparticles sinter
together to form a percolating skeleton, which hardens and stiffens
the adhesive. The tack adhesion is lost locally. Masks can be made
from silicone-coated disks, such as coins. Under the masks, adhesive
island regions are defined with the surrounding regions being a nontacky
coating. When optimizing the nanocomposite’s adhesive properties,
the addition of the hard nanoparticles raises the elastic modulus
of the adhesive significantly, but adhesion is not lost because the
yield point remains relatively low. During probe–tack testing,
the soft polymer phases yield and enable fibrillation. After heating
under IR radiation, the storage modulus increases by a factor of 5,
and the yield point increases nearly by a factor of 6, such that yielding
and fibrillation do not occur in the probe–tack testing. Hence,
the adhesion is lost. Loading and unloading experiments indicate that
a rigid skeleton is created when the nanoparticles sinter together,
and it fractures under moderate strains. This patterning method is
relatively simple and fast to execute. It is widely applicable to
other blends of thermoplastic hard nanoparticles and larger soft particles
Switching Off the Tackiness of a Nanocomposite Adhesive in 30 s via Infrared Sintering
Soft adhesives require an optimum balance of viscous
and elastic
properties. Adhesion is poor when the material is either too solidlike
or too liquidlike. The ability to switch tack adhesion off at a desired
time has many applications, such as in recycling, disassembly of electronics,
and painless removal of wound dressings. Here, we describe a new strategy
to switch off the tack adhesion in a model nanocomposite adhesive
in which temperature is the trigger. The nanocomposite comprises hard
methacrylic nanoparticles blended with a colloidal dispersion of soft
copolymer particles. At relatively low volume fractions, the nanoparticles
(50 nm diameter) accumulate near the film surface, where they pack
around the larger soft particles (270 nm). The viscoelasticity of
the nanocomposite is adjusted via the nanoparticle concentration.
When the nanocomposite is heated above the glass transition temperature
of the nanoparticles (<i>T</i><sub>g</sub> = 130 °C),
they sinter together to create a rigid network that raises the elastic
modulus at room temperature. The tackiness is switched off. Intense
infrared radiation is used to heat the nanocomposites, leading to
a fast temperature rise. Tack adhesion is switched off within 30 s
in optimized compositions. These one-way switchable adhesives have
the potential to be patterned through localized heating