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

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

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

Nonequilibrium Liquid–Liquid Phase Separation of Poly(<i>N</i>‑isopropylacrylamide) in Water/Methanol Mixtures

At room temperature, poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) is soluble in water and in methanol. Within intermediate mixing ratios of the two solvents, the PNIPAM coils collapse into insoluble globules, a phenomenon known as co-nonsolvency. Visual observation of mixed PNIPAM/water/methanol systems (polymer concentration ≥10 g L^–1, <i>M</i>_n 80 000 g L^–1) revealed that mixtures of methanol volume fractions (ϕ_M) ranging from 0.57 to 0.65 undergo macroscopic liquid–liquid phase separation (MLLPS) at 21 °C. MLLPS took place over a wider composition range (0.25 < ϕ_M < 0.60) for water/methanol mixtures containing a polymer sample bearing <i>n</i>-butyl end-groups (PNIPAM-45K (10.0 g L^–1, <i>M</i>_n 44 500 g mol^–1), but systems containing a polymer with chloroethyl end-groups (PNIPAM-Cl) (10.0 g L^–1, <i>M</i>_n 44 500 g mol^–1) did not undergo MLLPS over the entire mixing ratio span. Observation by fluorescence microscopy of a demixed PNIPAM-45K/water/methanol sample containing trace amounts of pyrene-labeled PNIPAM revealed that the rim of the heavy phase droplets is enriched in PNIPAM, which may affect the stability/coalescence of the droplets. ¹H NMR spectroscopy analysis of the heavy and light phases formed in demixed PNIPAM-45K/water/methanol samples indicated that the heavy liquid phase is enriched in PNIPAM and in water compared to the nominal composition of mixtures as prepared. A temperature/composition map (−40 °C < <i>T</i> < +45.5 °C) of PNIPAM-45K/water/methanol is reported, based on visual observations of samples prepared and stabilized at 21 °C. Interestingly, the macroscopically demixed samples were never transparent: one or both liquid phases remained cloudy or opaque independently of their history over experimentally undefined long times, implying that the samples reached metastability. The equilibrium state of lowest free energy that corresponds to the coexistence of two transparent phases was never attained

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

Additional file 1: of Size, Stability, and Porosity of Mesoporous Nanoparticles Characterized with Light Scattering

Contains following supplementary materials: fabrication of porous silicon nanoparticles, fabrication of silica nanoparticles, summary of silica nanoparticles' preparation conditions, summary of log-normal fitting results, absorbance of used nanoparticles, nitrogen sorption isotherms, additional TEM graphs from silica nanoparticles, fractal dimension analysis for SLS results and Kratky plots, all the studied correlations and measured zeta potential distributions. (DOCX 11779 kb

Thermally Sensitive Block Copolymer Particles Prepared via Aerosol Flow Reactor Method: Morphological Characterization and Behavior in Water

This work describes properties of thermosensitive submicrometer-sized particles having the same chemical composition but different morphologies. These particles have been prepared with an aerosol technique using dimethylformamide solutions of linear polystyrene-<i>block</i>-poly­(<i>N</i>-isopropylacrylamide)-<i>block</i>-polystyrene, PS-<i>b</i>-PNIPAM-<i>b</i>-PS. The particles were characterized by cryo-electron microscopy, microcalorimetry, and light scattering. Block copolymers self-assembled within the particles forming onion-like, gyroid-like, and spherical morphologies having poly­(<i>N</i>-isopropylacrylamide) matrix and physically cross-linking polystyrene domains. The particles were dispersed in aqueous media, and their behavior in water was studied both below and above the lower critical solution temperature of poly­(<i>N</i>-isopropylacrylamide). We found out that the particles with spherical and gyroid-like morphologies swell considerably in water at 20 °C, whereas at 40 °C the particles resemble more of those studied without water treatment. Light scattering experiments showed that the particles gradually aggregate and precipitate with time at 40 °C. Microcalorimetric studies revealed for all three studied morphologies that PNIPAM undergoes a two-step transition due to the different hydration levels of PNIPAM inside and outside the particles. Thicknesses of the PS and PNIPAM layers within the onion-like particles were analyzed using the TEM micrographs by fitting a model of electron density to the integrated electron intensity data. The surface layer of the particles was found out to be PNIPAM, which was supported by light scattering and microcalorimetry. It was also found out from the TEM micrograph analysis that the width of the outmost PS layer is considerably thinner than the one in the dry state prior to immersion in water, and a degradation scheme is proposed to explain these results

Thermally Sensitive Block Copolymer Particles Prepared via Aerosol Flow Reactor Method: Morphological Characterization and Behavior in Water

This work describes properties of thermosensitive submicrometer-sized particles having the same chemical composition but different morphologies. These particles have been prepared with an aerosol technique using dimethylformamide solutions of linear polystyrene-<i>block</i>-poly­(<i>N</i>-isopropylacrylamide)-<i>block</i>-polystyrene, PS-<i>b</i>-PNIPAM-<i>b</i>-PS. The particles were characterized by cryo-electron microscopy, microcalorimetry, and light scattering. Block copolymers self-assembled within the particles forming onion-like, gyroid-like, and spherical morphologies having poly­(<i>N</i>-isopropylacrylamide) matrix and physically cross-linking polystyrene domains. The particles were dispersed in aqueous media, and their behavior in water was studied both below and above the lower critical solution temperature of poly­(<i>N</i>-isopropylacrylamide). We found out that the particles with spherical and gyroid-like morphologies swell considerably in water at 20 °C, whereas at 40 °C the particles resemble more of those studied without water treatment. Light scattering experiments showed that the particles gradually aggregate and precipitate with time at 40 °C. Microcalorimetric studies revealed for all three studied morphologies that PNIPAM undergoes a two-step transition due to the different hydration levels of PNIPAM inside and outside the particles. Thicknesses of the PS and PNIPAM layers within the onion-like particles were analyzed using the TEM micrographs by fitting a model of electron density to the integrated electron intensity data. The surface layer of the particles was found out to be PNIPAM, which was supported by light scattering and microcalorimetry. It was also found out from the TEM micrograph analysis that the width of the outmost PS layer is considerably thinner than the one in the dry state prior to immersion in water, and a degradation scheme is proposed to explain these results

Supracolloidal Multivalent Interactions and Wrapping of Dendronized Glycopolymers on Native Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are high aspect ratio colloidal rods with nanoscale dimensions, attracting considerable interest recently due to their high mechanical properties, chirality, sustainability, and availability. In order to exploit them for advanced functions in new materials, novel supracolloidal concepts are needed to manipulate their self-assemblies. We report on exploring multivalent interactions to CNC surface and show that dendronized polymers (DenPols) with maltose-based sugar groups on the periphery of lysine dendrons and poly­(ethylene-<i>alt</i>-maleimide) polymer backbone interact with CNCs. The interactions can be manipulated by the dendron generation suggesting multivalent interactions. The complexation of the third generation DenPol (G3) with CNCs allows aqueous colloidal stability and shows wrapping around CNCs, as directly visualized by cryo high-resolution transmission electron microscopy and electron tomography. More generally, as the dimensions of G3 are in the colloidal range due to their ∼6 nm lateral size and mesoscale length, the concept also suggests supracolloidal multivalent interactions between other colloidal objects mediated by sugar-functionalized dendrons giving rise to novel colloidal level assemblies