Search results for "Amphiphile"

Detection of phase transitions in thin films with a quartz crystal microbalance

1996

Abstract The quartz crystal microbalance (QCM) is used to determine the phase transition point of thin films by measuring the change in frequency as a function of temperature. To elucidate this relationship, two types of polymers were studied where the bulk phase transitions were known. We investigated a casted thin film of an amphiphilic polyoxazoline and a Langmuir-Blodgett film comprised of fifteen double layers of an amphotropic polyacrylate. The phase transition points of the thin films could be detected by the QCM which were in the same range as for the bulk materials.

How Structure-Related Collapse Mechanisms Determine Nanoscale Inhomogeneities in Thermoresponsive Polymers

2012

Continuous wave electron paramagnetic resonance (CW EPR) spectroscopy on the amphiphilic spin probe TEMPO in solutions of selectively chosen functional, thermoresponsive poly(propylene oxide) (PPO)- and poly(ethylene oxide) (PEO)-based copolymers of both linear and branched structure is used to elucidate their host–guest interactions and inverse phase transitions. Three different fundamental types of host–guest interactions between probes and polymers could be correlated to the phase transition mechanisms (supported by MD simulations), evidencing that these proceed via nanoscale inhomogeneities of the polymers. Because of their ability to host small amphiphilic guest molecules, thermorespon…

Study of the micro-phase separation in LC-polymers with paired mesogens

1990

Differential scanning calorimetry and miscibility investigations were used to study the micro-phase separation of liquid-crystalline dimesogenic side-group polysiloxanes. Diluted co-polysiloxanes exhibit two glass transition temperatures and an unusual miscibility behavior. The observed biphasic character is compared with that of certain amphiphilic systems.

Photosensitive functionalized surface-modified quantum dots for polymeric structures via two-photon-initiated polymerization technique.

2015

In this paper, the surface modification of CdSe- and CdZnS-based quantum dots (QDs) with a functional silica shell is reported. Functionalized silica shells are prepared by two routes: either by ligand exchange and a modified Stober process or by a miniemulsion process with amphiphilic poly(oxyethylene) nonylphenylether also know as Igepal CO-520 (IG) as oligomeric amphiphile and modified silica precursors. The polymerizable groups on the functionalized silica shell allow covalent bonding to a polymer matrix and prevent demixing during polymerization and crosslinking. This allows the homogeneous incorporation of QDs in a crosslinked polymer matrix. This paper furthermore demonstrates that t…

Polymer-induced shape changes and capping in giant liposomes

1995

We studied the coupling of a polymeric amphiphile undergoing a transition from an expanded to a collapsed state of the hydrophilic polymer chain upon heating above 29°C with free and solid supported lipid bilayers. Lateral diffusion measurements and studies of vesicle shape-changes confirmed previous calorimetric studies, suggesting that the amphiphile remains incorporated in the giant vesicles and the supported bilayer during the transition. The two-dimensional hydrodynamic radii of the amphiphile in the expanded and collapsed state was measured by making use of the strong quadratic dependence of the diffusion coefficient on the radius of the diffusant (D ∞ r−2) due to the frictional coupl…

1995

Polystyrene-block-poly-1-azabicyclooctane[4,2,0] has been modified by protonation or alkylation of the polyamine moiety. Short chain alkyl iodides lead to quantitatively quarternized products while longer alkyl chains or alkyl-bromides give incomplete conversion. The viscosimetric behavior of the charged blockcopolymers is dominated by the polyelectrolyte block although the polyelectrolyte effect is drastically reduced by the presence of the polystyrene block. The blockcopolymers are insoluble in water, but concentrated solutions of the polymers in DMF can be diluted with any amount of water without any precipitation. Although the blockcopolymers have an amphiphilic structure they do not ex…

Role of Topology and Amphiphilicity for Guest Encapsulation in Functionalized Hyperbranched Poly(ethylenimine)s

2004

The promising potential of dendrimers in a variety of areas, such as catalysis, materials science and biomedicine is related to their globular shape, large number of modifiable surface functionalities and the presence of internal reservoirs.1 Their use in liquidliquid-phase transfer protocols, based on the encapsulation of guest molecules as drug delivery vehicles for pharmaceutical application, represents an important issue.2 Unfortunately, dendrimer synthesis is timeconsuming, which currently limits practical use to laboratory scale. For that reason, hyperbranched polymers prepared from ABm-type monomers in one-step processes have gained increasing interest.3 The development of the slow m…

Combining oxyanionic polymerization and click-chemistry: a general strategy for the synthesis of polyether polyol macromonomers

2014

We describe a synthetic pathway to tailor-made amphiphilic macromonomers by a combination of anionic ring-opening polymerization and copper-catalyzed azide–alkyne cycloaddition (CuAAC). Linear polyglycerol and poly(glyceryl glycerol) were synthesized in a controlled manner by anionic ring-opening polymerization of ethoxyethyl glycidyl ether or isopropylidene glyceryl glycidyl ether, respectively, with narrow and monomodal molecular weight distributions (Mw/Mn < 1.20) and molecular weights ranging from 850 g mol−1 to 2500 g mol−1. After end-capping with propargyl bromide and removal of the protecting groups, the hydrophilic precursors were quantitatively clicked to a series of hydrophobic az…

Structural variations in amphiphiles: Discoidal multivalent cations

1986

Fourteen cationic multipolar amphiphiles have been synthesized with pyridinium or trimethylammonium head groups. The hydrophobic cores are planar ring systems (benzene or triphenylene) to which two, three, four, or six decylene or undecylene alkyl chains are attached by ester linkages. The hydrophilic head groups are bound to the outer ends of the alkyl chains.

Oxidation-responsive polyether block copolymers lead to non-ionic polymer surfactants with multiple amine N-oxides

2019

Block copolymers consisting of a nonpolar poly(propylene oxide) block and a poly(glycidyl amine) block were prepared by anionic ring-opening polymerization (AROP). The tertiary amine groups of the block copolymers were quantitively transformed into the corresponding zwitterionic amine N-oxides, as confirmed by 1H NMR and 15N NMR spectroscopy. This leads to strongly amphiphilic polyether block copolymers with multiple N-oxides. Full oxidation of the amine groups was also possible in situ in an emulsion, demonstrating the oxidation-responsive character of this new class of non-ionic polymeric surfactants.