Counterion-Induced UCST for Polycations

A method to promote upper critical solution temperature (UCST) type of behavior for polycations is introduced. This relies on <i>in situ</i> introduction of a hydrophobic anion to an aqueous solution of a polycation in the presence of sufficient ionic strength. This was studied using two polycations: poly­(2-methacryl­oyloxyethyl­trimethylammonium iodide) and poly­(3-methyl-1-(4-vinylbenzyl)­imidazolium chloride). The solution behavior of the polymers was investigated in the presence of bis­(trifluoromethane)­sulfonamide (NTf₂) and trifluoromethanesulfonate (OTf), adjusting the ionic strength with sodium chloride. All the four studied cation–anion pairs undergo an UCST type phase separation. The phase separation was reversible and only very weakly dependent on polymer concentration in the studied range

Using Light To Tune Thermo-Responsive Behavior and Host–Guest Interactions in Tegylated Poly(azocalix[4]arene)s

Polymers consisting of azocalix[4]­arenes in the main chain and tetraethylene glycol monomethyl ether chains in the lower rim of the calix[4]­arene units have been prepared. The polymers undergo reversible photoisomerization between the <i>trans</i> and the <i>cis</i> forms, the extent of which depends on the solvent. A lower critical solution temperature (LCST) type behavior is observed for aqueous solutions of the polymers, which is strongly affected by the molar mass and concentration. More importantly, the same polymers exhibit an upper critical solution temperature (UCST) type transition in alcohols. It is shown that the temperature of the phase transition in alcohols decreases proportionally to the decrease in the <i>trans</i> content of the samples thus offering a unique possibility to reversibly tune the UCST behavior by adjusting the irradiation exposure time. An exciting photoassisted writing on solutions of the polymer in alcohols is demonstrated. Furthermore, the host–guest complex formation with a low molar mass guest is influenced by the photostationary state of the polymers

Influence of Hydrophobic Anion on Solution Properties of PDMAEMA

The effect of bis­(trifluoromethane)­sulfonimide, NTf₂, anion on solution properties of the thermoresponsive poly­(2-(dimethylamino)­ethyl methacrylate), PDMAEMA, has been studied. Nonstoichiometric amounts of LiNTf₂ were added to aqueous solutions of PDMAEMA, with or without a buffer in the pH range 6–10. Since PDMAEMA is a weak polybase, the interaction between PDMAEMA and NTf₂ can be manipulated by the concentration of the anion and also by varying the degree of charging of PDMAEMA with pH. PDMAEMA has a well-known LCST behavior which can be modulated by the counterion. It was observed that the hydrophobic NTf₂ anion not only decreases the cloud point of PDMAEMA but also triggers an upper critical solution temperature (UCST) type behavior in acidic pH. In a higher pH regime, NTf₂ makes the cloud point increase because the anion turns PDMAEMA to a stronger base, presumably by effectively shielding the charges

Thermoresponsive Nanoparticles of Self-Assembled Block Copolymers as Potential Carriers for Drug Delivery and Diagnostics

Thermally responsive hydrogel nanoparticles composed of self-assembled polystyrene-<i>b</i>-poly­(<i>N</i>-isopropylacrylamide)-<i>b</i>-polystyrene block copolymers and fluorescent probe 1-anilinonaphthalene-8-sulfonic acid have been prepared by aerosol flow reactor method. We aimed exploring the relationship of intraparticle morphologies, that were, PS spheres and gyroids embedded in PNIPAm matrix, as well PS–PNIPAm lamellar structure, to probe release in aqueous solution below and above the cloud point temperature (CPT) of PNIPAm. The release was detected by fluorescence emission given by the probe binding to bovine serum albumin. Also, the colloidal behavior of hydrogel nanoparticles at varying temperatures were examined by scattering method. The probe release was faster below than above the CPT from all the morphologies of which gyroidal morphology showed the highest release. Colloidal behavior varied from single to moderately aggregated particles in order spheres-gyroids-lamellar. Hydrogel nanoparticles with tunable intra particle self-assembled morphologies can be utilized designing carrier systems for drug delivery and diagnostics

Inkjet-Printed Gold Electrodes on Paper: Characterization and Functionalization

Gold nanoparticles were synthesized and inkjet-printed on a paper substrate and IR-sintered to produce conductive electrodes. The electrodes were further functionalised by using self-assembled octadecanethiol monolayers (SAMs). The effect of sintering, print quality, and SAM formation were examined by topographical, chemical and electrical methods. With optimised printing parameters, a volume resistivity of ∼1.6 ×10^–7 Ω m was attained by a single print layer

Inkjet-Printed Gold Electrodes on Paper: Characterization and Functionalization

Gold nanoparticles were synthesized and inkjet-printed on a paper substrate and IR-sintered to produce conductive electrodes. The electrodes were further functionalised by using self-assembled octadecanethiol monolayers (SAMs). The effect of sintering, print quality, and SAM formation were examined by topographical, chemical and electrical methods. With optimised printing parameters, a volume resistivity of ∼1.6 ×10^–7 Ω m was attained by a single print layer

Control of the Morphology of Lipid Layers by Substrate Surface Chemistry

In this study, surface coatings were used to control the morphology of the deposited lipid layers during vesicle spreading, i.e., to control if liposomes self-assemble on a surface into a supported lipid bilayer or a supported vesicular layer. The influence of the properties of the surface coating on formation of the deposited lipid layer was studied with quartz crystal microbalance and two-wavelength multiparametric surface plasmon resonance techniques. Control of lipid self-assembly on the surface was achieved by two different types of soft substrate materials, i.e., dextran and thiolated polyethylene glycol, functionalized with hydrophobic linkers for capturing the lipid layer. The low-molecular-weight dextran-based surface promoted formation of supported lipid bilayers, while the thiolated polyethylene glycol-based surface promoted supported vesicular layer formation. A silicon dioxide surface was used as a reference surface in both measurement techniques. In addition to promoting supported lipid bilayer formation of known lipid mixtures, the dextran surface also promoted supported lipid bilayer formation of vesicles containing the cell membrane extract of human hepatoblastoma cells. The new dextran-based surface was also capable of protecting the supported lipid bilayer against dehydration when exposed to a constant flow of air. The well-established quartz crystal microbalance technique was effective in determining the morphology of the formed lipid layer, while the two-wavelength surface plasmon resonance analysis enabled further complementary characterization of the adsorbed supported lipid bilayers and supported vesicular layers

Interfacial and Fluorescence Studies on Stereoblock Poly(<i>N</i>‑isopropylacryl amide)s

Aqueous solution and water–air interfacial properties of associative thermally responsive A–B–A stereoblock poly­(<i>N</i>-isopropylacryl amide), PNIPAM, polymers were studied and compared to atactic PNIPAM. The A–B–A polymers consist of atactic PNIPAM as a hydrophilic block (either A or B) and a water-insoluble block of isotactic PNIPAM. The surface tensions of aqueous PNIPAM solutions were measured as a function of both temperature and concentration. The isotactic blocks did not have an effect on the surface activity of the solutions. Rheological measurements on the water–air interface showed that the aggregated PNIPAMs containing isotactic blocks increased the elasticity of the surface significantly as compared to the atactic reference upon heating. Two fluorescence probes, pyrene and (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4<i>H</i>-pyran (4HP), added to the aqueous polymer solutions were concluded to reside in surroundings with lower polarity and increased microviscosity in cases when the polymers contained isotactic blocks, as compared to ordinary atactic polymers

Thermoresponsiveness of PDMAEMA. Electrostatic and Stereochemical Effects

Isotactic triads are introduced into poly­(dimethylaminoethyl methacrylate) (PDMAEMA) when a Lewis acid yttrium­(III)­trifluoromethanesulfonate, Y­(OTf)₃, is present during the ATRP polymerization. The changes in the tacticities of the polymers are modest. However, the tacticity affects the phase separation process but in a different way in two studied cases, at pH 8 and 9. The pH, and thus the charge of the polymer, affects the balance between electrostatic and stereochemical effects. Upon the chain collapse, the zeta potential of the polymer decreases discontinuously at pH 9, whereas at pH 8 the potential keeps almost constant. However, even in the latter case the influence of the isotactic segments on the thermal transition may be observed. Increasing isotacticity is suggested to decrease the flexibility of the polymer chain. It also causes the polymers to adsorb in a more organized manner to the air/water interface than the atactic ones do. The change in the thermoresponsive behavior due to the changing tacticity of the polymer has been studied at the interface by observing the surface tension and by surface rheology and in the solution by conventional rheology. Differences in the elastic and viscous moduli owing to the different tacticities of the polymers are compared to those attributed to different molar masses and to varying pH

Simple and Efficient Separation of Atomically Precise Noble Metal Clusters

There is an urgent need for accessible purification and separation strategies of atomically precise metal clusters in order to promote the study of their fundamental properties. Although the separation of mixtures of atomically precise gold clusters Au₂₅L₁₈, where L are thiolates, has been demonstrated by advanced separation techniques, we present here the first separation of metal clusters by thin-layer chromatography (TLC), which is simple yet surprisingly efficient. This method was successfully applied to a binary mixture of Au₂₅L₁₈ with different ligands, as well as to a binary mixture of different cluster cores, Au₂₅ and Au₁₄₄, protected with the same ligand. Importantly, TLC even enabled the challenging separation of a multicomponent mixture of mixed-monolayer-protected Au₂₅ clusters with closely similar chemical ligand compositions. We anticipate that the realization of such simple yet efficient separation technique will progress the detailed investigation of cluster properties