Heliconal nematic twist bend (NTB) phases are usually not well oriented in planar commercial cells, even in thin (~1 µm) ones where a micron-sized periodic texture is usually observed [1,2,3] (see Fig.1-a). The origin of the stripe patterns is attributed to the rapid shrinking of the pseudo-layers below the N-NTB phase transition temperature, which yields an undulation instability. The observed periodicity is found to be twice the cell gap [1].
We have explored the effect of the strength of the anchorings of the substrates on the resulting patterns. We used polymer aligning layers of tunable azimuthal and zenithal strengths to design liquid crystal cells with surface anchorings ranging from ultraweak to strong. We then have studied the patterns formed by the NTB phase of 1,7-bis-4-(4-cyanobiphenyl) heptane (CB7CB). We will show how the period of the stripes can be varied in a large range in cells of the same thickness but with different anchoring preparations. With adequate anchoring conditions (see Fig.1-b-c), an excellent and spontaneous planar alignment of the NTB phase of CB7CB can be obtained much below the phase transition temperature.
[1] Panov V.P. et al; Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogenswith a Nematic-Nematic Transition and a Negative Elastic Constant; Phys. Rev. Lett. ; 105; 167801; 2010.
[2] Challa P. K. et al; Twist-bend nematic liquid crystals in high magnetic fields; Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys.; 89; 060501; 2014.
[3] Vaupotič N. et al.; Polarization Gratings Spontaneously Formed from a Helical Twist‐Bend Nematic Phase; Chem. Phys. Chem.; 19; 2566; 2018.

Heliconal nematic twist bend (NTB) phases are frequently found at high temperatures. In the last years the search of stable room-temperatures NTB phases has led to the synthesis of new compounds [1] and to the design of multicomponent systems. Mixtures of NTB compounds with nematogens ,such as 4-Cyano-4'-pentylbiphenyl (5CB) dimeric liquid crystal 1,7-bis(4-cyanobiphenyl-4-yl) heptane (CB7CB) decrease strongly the temperature range of the NTB phase and tune the optical, thermal and dielectric properties of NTB [2]. In this work we have explored the physical properties of mixtures of CB7CB with several smectogens with a particular focus on 4′-octyl-4-biphenylcarbonitrile (8CB). The 8CB/CB7CB phase diagram reveals striking features compared to the 5CB/CB7CB one. Despite their macroscopic resemblance, SmA and NTB domains appear incompatible and remain separated by a nematic phase that extends to very low temperature (-20°C) at a CB7CB fraction of ϕ_c≈20%. We have characterized the optical, thermal, dielectric and anchoring properties of the N and NTB phases of the mixtures. Compared to the pure CB7CB system, the N phase shows unusual behavior over a large range of composition and reveals strong pre-transitional effects when approaching ϕ_c. We also found that, for specific aligning substrates, adding 8CB to CB7CB drastically changes the anchoring properties (fig1) facilitating homeotropic alignment.
[1] Yuan Wang, Quan Li; Room temperature heliconical twist-bend nematic liquid crystal; Cryst. Eng. Comm; 17; 2778-2782; 2015.
[2] Nina Trbojevic and Mamatha Nagaraj; Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases; Phys. Rev. E ;96; 052703; 2017.

The conformation of single-chain nanoparticles (SCNPs) in presence of linear polystyrene crowding molecules has been studied by small-angle neutron scattering under contrast-matching of the crowders. A model describing the scattering of aggregating polydisperse SCNPs has been developed, resulting in the determination of the potentially squeezed size of the individual SCNPs within aggregates, their local chain statistics, and the average aggregation number, as a function of crowding. Two different crowders – of low and high molecular weight, respectively – are shown to have a different effect: while long chains tend to impede their aggregation above their overlap concentration, short ones are found to mediate depletion interactions leading to aggregation. Self-imposed crowding within the aggregates has a similar impact on chain conformation independently of the crowding of the surrounding medium. Our results are compared to recent simulations and shall contribute to the microscopic understanding of the phase behavior of soft intrinsically disordered nano-objects, and in particular the effect of crowding on biomacromolecules.

The dynamic and static properties of the interfacial region between polymer and nanoparticles have wide-ranging consequences on performances of nanomaterials. The thickness and density of the static layer are particularly difficult to assess experimentally due to superimposing nanoparticle interactions. Here, we tune the dispersion of silica nanoparticles in nanocomposites by pre-adsorption of polymer layers in the precursor solutions, and by varying the molecular weight of the matrix chains. Nanocomposite structures ranging from ideal dispersion to repulsive order or various degrees of aggregation are generated and observed by small-angle scattering. Pre-adsorbed chains are found to promote ideal dispersion, before desorption in the late stages of nanocomposite formation. The microstructure of the interfacial polymer layer is characterized by detailed modeling of X-ray and neutron scattering. Only in ideally well-dispersed systems a static interfacial layer of reduced polymer density over a thickness of ca. 2 nm is evidenced based on the analysis with a form-free density profile optimized using numerical simulations. This interfacial gradient layer is found to be independent of the thickness of the initially adsorbed polymer, but appears to be generated by out-of-equilibrium packing and folding of the pre-adsorbed layer. The impact of annealing is investigated to study the approach of equilibrium, showing that initially ideally well-dispersed systems adopt a repulsive hard-sphere structure, while the static interfacial layer disappears. This study thus promotes the fundamental understanding of the interplay between effects which are decisive for macroscopic material properties: polymer-mediated interparticle interactions, and particle interfacial effects on surrounding polymer.

Tackling the question of specific interactions in a complex blend of Proteins. Edible Soft Matter – a SoftComp Topical Workshop