Crystal Superstructure Research Articles

Enhancing mechanical performance of polylactide by tailoring crystal morphology and lamellae orientation with the aid of nucleating agent

The performance of semicrystalline polymers is significantly dependent on the crystal morphology and lamellae orientation. In this work, the crystal superstructure and mechanical properties of polylactide (PLA) with different amounts of nucleating agent (tetramethylene-dicarboxylic dibenzoyl-hydrazide, TMC-306) were investigated. It was found that TMC-306 can be dissolved in PLA melt and re-crystallize into fibrils upon cooling. These fibrils can serve as nucleation templates to induce the crystallization of PLA on their surface, resulting in a large enhancement in crystallization rate. More importantly, PLA lamellae can grow perpendicular to the long axis of TMC-306 fibrils, inducing the formation of shish-calabash, shish-kebab and needle-like structures, depending on the concentration of TMC-306 used. Taking advantage of shear flow experienced in injection molding, TMC-306 fibrils tend to align in PLA melt along the shear flow direction, inducing the formation of highly orientated PLA lamellae in injection-molded articles. In this way, a simultaneous improvement in impact toughness, tensile strength and elongation at break is achieved. This work provides a good example of using a fibrous nucleating agent as a template to tailor the crystal morphology and lamellae orientation, thus achieving greatly enhanced properties for PLA.

Significantly Improving Oxygen Barrier Properties of Polylactide via Constructing Parallel-Aligned Shish-Kebab-Like Crystals with Well-Interlocked Boundaries

Recently, some attempts have been made to enhance the gas barrier properties of semicrystalline polymers by precisely controlling the arrangement of their impermeable crystalline lamellae. However, it is still a great challenge to achieve regular arrangement of the lamellae along the direction perpendicular to the gas diffusion path, especially using conventional polymer processing technologies. This work presents a novel and simple strategy to dramatically improve oxygen barrier performance of biobased and biodegradable polylactide (PLA) through constructing parallel-aligned shish-kebab-like crystals with well-interlocked boundaries with the aid of a highly active nucleating agent. The nucleating agent was introduced into PLA by melting compounding and the sheet-like specimens were fabricated by compression molding. We demonstrate that the fibrillar nucleating agent dispersed in PLA melt can serve as shish to induce the change of crystallization habit of PLA from isotopic spherulitic crystals to unique shish-kebab-like crystals and the shear flow in the compression molding can induce the highly ordered alignment of the nucleating agent fibrils as well as the subsequent shish-kebab-like crystals along the direction parallel to the sheet surface. More importantly, the growing lamellae are found to interpenetrate and tightly interlock with each other at the boundary regions of the shish-kebab-like crystals in the later stage of the crystallization, forming a densely packed nanobrick wall structure to prevent gas molecules from permeating through the crystals and thus imparting the PLA sheets with unprecedentedly low oxygen permeability. This work provides not only a successful example of preparing semicrystalline polymer with super gas barrier properties by tailoring crystal superstructure but also a promising route to rapidly fabricate high-performance food packaging materials via industrially meaningful melt processing.

Formation and Alignment of Hybrid Shish-Kebab Morphology with Rich Beta Crystals in an Isotactic Polypropylene Pipe

In this work we successfully controlled formation and alignment of a crystal superstructure in an isotactic polypropylene (iPP) pipe via self-assembly of a β nucleating agent and rotation extrusion to tailor the performances of the iPP pipe. The results showed that during iPP pipe extrusion, β nucleating agents first self-assembled into the fibrous structure, and then were aligned off the axial direction through rotation of the mandrel and die in the self-designed rotation extrusion device. Accordingly, fibrils, as oriented templates, directed the epitaxial growth of iPP to yield hybrid shish-kebabs off the axial direction which was composed of β crystals, so as to achieve simultaneous hoop reinforcement and toughening of the iPP pipe.

A neutron diffraction study of the R15Ge9C compounds (R = Ce, Pr, Nd)

In this work we report the results of the neutron diffraction investigation performed on the germanides R15Ge9C, for R=Ce, Pr and Nd (La15Ge9Fe-type, hP50, P63mc, Z=2), to refine the crystal superstructure of these compounds and determine their magnetic structures. The interstitial carbon atoms occupy mainly the 2b Wyckoff site in the position (1/32/3∼1/2) and also, with a smaller occupancy rate, the Wyckoff site 2a at (00∼1/2). In the magnetic state, the three compounds display predominantly a ferromagnetic behavior with the propagation vector k=[000]. These results are in agreement with the magnetization measurements, with TC=10, 30 and 80K as Curie temperature of Ce15Ge9C, Pr15Ge9C and Nd15Ge9C, respectively. Ce15Ge9C and Nd15Ge9C present a ferromagnetic alignment of the R moments along the c-axis and an antiferromagnetic spin arrangement within the (a–b) plane. For Pr15Ge9C the ferromagnetic contribution is found within the (a–b) plane, as previously observed for the isotypic compound Tb15Si9C. The carbides crystal structure possesses four inequivalent rare earth sites carrying different magnetic moments, leading to mean values of 0.9μB/Ce, 1.1μB/Pr and 2.2μB/Nd for Ce15Ge9C, Pr15Ge9C and Nd15Ge9C, respectively.The magnetic structures of these R15Ge9C compounds differ strongly from those of their parent R5Ge3 germanides, but present strong similarities with the structures of the R15Si9C compounds. The overall results indicate and confirm the drastic influence of carbon insertion in the rare earth environment.

Synthesis and Self‐Assembled Helical Supramolecular Polymer of Ethyl 7,8‐dihydro‐3‐hydroxy‐9‐methyl‐7‐(4′‐nitrophenyl)‐6H‐dibenzo[c]‐ pyran‐6‐one‐8‐carboxylate

ABSTRACTA structurally novel compound was isolated as the main product of tandem Pechmann–dehydration between diethyl 4‐hydroxy‐4‐methyl‐2‐(4′‐nitrophenyl)‐6‐oxocyclohexane‐1,3‐dicarboxylate (1) and resorcinol in the presence of trifluoroacetic acid. The structure of the product was determined as a racemate of (7R,8R)‐ and (7S,8S)‐ethyl 7,8‐dihydro‐3‐hydroxy‐9‐methyl‐7‐(4′‐nitrophenyl)‐6H‐dibenzo[c]‐pyran‐6‐one‐8‐carboxylate (3a) enantiomers by single crystal X‐ray diffraction analysis. The X‐ray crystal structure revealed that 3a possesses an extended and more stable conjugated aromatic system as a consequence of the stereoselectivity of intramolecular dehydration behavior of Pechmann condensation product 2. In the crystal superstructure, the (7R,8R)‐ and (7S,8S)‐isomers of 3a respectively self‐assembled into left‐ and right‐handed supramolecular helical chains with a channel size of 3.70 Å × 10.20 Å in virtue of intermolecular hydrogen bonding together with dramatic twisting between carboxylate group at C8 and tricyclic ring framework of 3a, which are then arranged alternatively along the b‐axis direction with a pitch length of 7.894 Å.

In Situ Surface X-Ray Diffraction Studies of the Influence of the PEG-Cl-Complex on Homoepitaxial Electrodeposition on Cu(001)

The influence of polyethylene glycol (PEG) on the atomic-scale interface structure and Cu growth behavior of Cu(001) in chloride-containing electrolyte was investigated by in situ surface X-ray diffraction. Studies in Cu-free solution unambiguously verify the presence of the ordered c(2 × 2) chloride adlayer in the presence of the polymer as well as reversible Cl adsorption/desorption and an order-disorder transition in the adlayer. The partially ordered chloride adlayer is found over a wider potential range as compared to PEG-free electrolyte, indicating stabilization of this adsorbate phase. Crystal truncation and superstructure rod measurements reveal that the polymer interacts more strongly with the partially c(2 × 2) Cl covered surface than with the close-packed c(2 × 2) adlayer at saturation coverage. In Cu-containing electrolyte layer-by-layer growth was observed at potentials ≤ −0.35 V vs. Ag/AgCl. The deposition rate was significantly reduced as compared to PEG-free electrolyte, providing clear evidence of inhibition on the atomic-scale. At more positive potentials a crossover to 3D growth and increasing surface roughness is found.

Mineralization of unique barium carbonate crystal superstructures controlled by a liquid crystalline phase polymer

Barium carbonate (BaCO3) crystals with unique hierarchical superstructures have been fabricated through a facile and controlled solution self-assembly mode in the presence of a tri-block copolymer PEO70–PPO20–PEO70 (P123). The powder X-ray diffraction (XRD) results revealed that the obtained BaCO3 product was indexed to pure orthorhombic phase. Notably, BaCO3 samples with well-defined hierarchical morphologies, including spherical, rod, hexangular prism, and porous spherical aggregates can be prepared by simply adjusting the polymer P123 concentrations and the ratios of [Ba2+]/[P123]. Specifically, layered screw cap, double-taper, and shuttle-shaped superstructures were formed through choosing N,N-bimethylformamide (DMF), tetrahydrofuran (THF), and/or toluene mixed with de-ionised water (DIW) as the reaction media in the current system, respectively. It is clearly demonstrated that varying liquid crystal-phase aggregating structures of the polymer P123 and using different solvents can indeed exert a significant influence over the selective nucleation, crystal facets preferable adsorption, and consequent over-growth for the BaCO3 primary particles. Moreover, a possible formation process for the hierarchical superstructures of BaCO3 crystals is proposed.

Method of enumeration of crystal superstructures based on fcc, bcc, and hexagonal close packings

A new method of enumeration of crystal superstructures is described. It involves (a) constructing of superlattices using Hermite Normal Form, (b) generating of superstructures by labeling of points of the base lattice, with non-unique solutions sorted off, (c) reducing the primitive cell of a superlattice to the Niggli cell, (d) assigning a Bravais lattice type to superlattice and changing the supercell to a standard setting of Bravaise basis vectors, (e) calculating the space group symmetry of the superstructure using the CRYCOM program of crystal structure comparison. The geometrical and symmetrical characteristics has been presented for the superlatices derived from the fcc, bcc and hcp types of the base lattice. As an application of the present method, the critical compositions of Fe-Cr alloys observed in studies of pitting corrosion has been explained as being conformed with the conditions of ordered superstructure formation giving rise to characteristic crystallographic symmetries.

Effect of crystal habit and superstructure on modulus of elasticity of isotactic polypropylene by AFM nanoindentation

In this study the effects of crystal habit, crystallinity and superstructure on the modulus of elasticity of isotactic polypropylene films were analyzed by atomic force microscope (AFM) nanoindentation. The modulus of elasticity, evaluated on the nanometer scale by AFM, showed a qualitatively similar dependence on the crystal habit, crystallinity and superstructure as the modulus of elasticity measured by dynamic-mechanical analysis and tensile testing. The observed values of both the surface stiffness measured by AFM and the macroscopic/bulk stiffness were distinctly larger in the presence of non-isometric lamellae organized in spherulite than in the presence of isometric nodular crystals, not organized in a spherulitic superstructure. The experimental data showed that the modulus of elasticity is not primarily influenced by the presence or absence of spherulite but by the molecular-deformation constraint associated to the crystal habit.

Control of Crystal Morphology in Poly(l-lactide) by Adding Nucleating Agent

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTControl of Crystal Morphology in Poly(l-lactide) by Adding Nucleating AgentHongwei Bai, Weiyi Zhang, Hua Deng*, Qin Zhang, and Qiang Fu*View Author Information College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, P. R. China*Tel/Fax +86 28 8546 1795, e-mail [email protected] (Q.F.); e-mail [email protected] (H.D.).Cite this: Macromolecules 2011, 44, 6, 1233–1237Publication Date (Web):February 14, 2011Publication History Received26 October 2010Revised14 January 2011Published online14 February 2011Published inissue 22 March 2011https://doi.org/10.1021/ma102439tCopyright © 2011 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views3165Altmetric-Citations177LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (2 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Crystal structure,Crystallization,Crystals,Morphology,Nanofibers Get e-Alerts

Ultra-smooth lithium niobate photonic micro-structures by surface tension reshaping

Annealing of micro-structured lithium niobate substrates at temperatures close to, but below the melting point, allows surface tension to reshape preferentially melted surface zones of the crystal. The reshaped surface re-crystallizes upon cooling to form a single crystal again as it is seeded by the bulk which remains solid throughout the process. This procedure yields ultra-smooth single crystal superstructures suitable for the fabrication of photonic micro-components with low scattering loss.

Deuterated Water Effect in a Room Temperature Ionic Liquid: N,N-Diethyl-N-methyl-N-2-methoxyethyl Ammonium Tetrafluoroborate

A deuterated water effect in the room temperature ionic liquid (RTIL) N,N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate, [DEME][BF(4)], is observed in its crystal domain structures; crystallization temperature, T(c); crystal superstructures; and volume contractions. The above effect, seen in [DEME][BF(4)]-0.9 mol % H(2)O mixtures, is reduced in 1.0 mol % 0.75 H(2)O x 0.25 D(2)O and 0.9 mol % 0.5 H(2)O x 0.5 D(2)O mixtures and is completely suppressed in 1.3 mol % D(2)O mixtures. Interestingly, T(c) decreased systemically with D substitutions of water. In contrast to the crystal state, it was found that there is no difference between H(2)O and D(2)O mixtures in the liquid state, on the basis of X-ray diffraction patterns. At around 80-90 mol % H(2)O, the intermolecular correlation of [DEME][BF(4)] as a local structure changes to that of bulk water.

Low temperature structure of FeSr2YCu2O6+δ magnetic superconductor

FeSr2YCu2O6+δ with the tetragonal Ba2YCu3O6+δ-type structure exhibits superconductivity around 60K, when it is properly annealed in N2 and subsequently in O2. This compound also exhibits antiferromagnetic order of Fe around 20K. We have performed neutron powder diffraction of the FeSr2YCu2O6+δ system at low temperature to investigate the relation between the crystal structure and the physical properties. Neutron diffraction study indicates that this compound does not have the structure phase transition due to the tilt of the FeO6 octahedron differently from the RuSr2GdCu2O8 magnetic superconductor with the same structure, and that the magnetic order in FeSr2YCu2O6+δ is not long-range order, because we can observe no extra reflection due to the crystal and magnetic superstructure.

Rigid‐Strut‐Containing Crown Ethers and [2]Catenanes for Incorporation into Metal–Organic Frameworks

To introduce crown ethers into the struts of metal-organic frameworks (MOFs), general approaches have been developed for the syntheses of dicarboxylic acid dibenzo[30]crown-10 (DB30C10DA), dicarboxylic acid di-2,3-naphtho[30]crown-10 (DN30C10DA), dicarboxylic acid bisparaphenylene[34]crown-10 (BPP34C10DA), and dicarboxylic acid 1,5-naphthoparaphenylene[36]crown-10 (NPP36C10DA). These novel crown ethers not only retain the characteristics of their parent crown ethers since they can 1) bind cationic guests and 2) serve as templates for making mechanically interlocked molecules (MIMs), such as catenanes and rotaxanes, but they also present coordination sites to connect with secondary building units (SBUs) in MOFs. The binding behavior of BPP34C10DA with 1,1'-dimethyl-4,4'-bipyridinium bis(hexafluorophosphate) (DMBP2.PF(6)) has been investigated by means of UV/Vis, fluorescence, and NMR spectroscopic techniques. The crystal superstructure of the complex DMBP2.PF(6) subset BPP34C10DA was determined by X-ray crystallography. The NPP36C10DA-based [2]catenane (H(2)NPP36C10DC-CAT4.PF(6)) and the BPP34C10DA-based [2]catenane (H(2)BPP34C10DC-CAT4.PF(6)) were prepared in DMF at room temperature by the template-directed clipping reactions of the planarly chiral NPP36C10DA and BPP34C10DA with 1,1'-[1,4-phenylenebis(methylene)]di-4,4'-bipyridin-1-ium bis(hexafluorophosphate) and 1,4-bis(bromomethyl)benzene, respectively. The crystal structure of the dimethyl ester (BPP34C10DE-CAT4.PF(6)) of the [2]catenane H(2)BPP34C10DC-CAT4.PF(6) was investigated by X-ray crystallography, which revealed racemic R and S isomers with planar chirality present in the crystal in a 1:1 ratio. These crown ether based struts serve as excellent organic ligands to bind with transition metal ions in the construction of MOFs: the crown ethers BPP34C10DA and NPP36C10DA in the presence of Zn(NO(3))(2)4.H(2)O afforded the MOF-1001 and MOF-1002 frameworks, respectively. The crystal structures of MOF-1001 and MOF-1002 are both cubic and display Fm3m symmetry. The unit cell parameter of the metal-organic frameworks is a=52.9345 A. Since such MOFs, containing electron-donating crown ethers are capable of docking incoming electron-accepting substrates in a stereoelectronically controlled fashion, the present work opens a new access to the preparation and application of MOFs.

Half Antiperovskites: IV. Crystallographic and Electronic Structure Investigations onA2Rh3S2(A= In, Sn, Tl, Pb, Bi)

AbstractThe crystal and electronic structures of ordered half antiperovskitesA2Rh3S2=ARh3/2S (A= In, Sn, Tl, Pb, Bi) are investigated. From powder and single crystal data superstructures, rhodium site ordering, trends in bonding and coordination are analysed with respect to theAsite atom. Comparisons address isotypic and isoelectronic relations to monoclinic parkerite (Bi2Ni3S2) type superconductors, the trigonal half‐metal ferromagnet Sn2Co3S2, and rhodium‐containing antiperovskites. Local structure and bonding is analysed with respect to the ordered occupation of half of S2A4sites (= perovskite oxygen sites) and interlinking to 2D networks [Rh3S2]∞δ–by face‐, edge‐ and corner‐sharing. The theoretical part includes DFT band structure and ELF calculations, systematic comparisons to rhodium and antiperovskites, as well as spin‐polarised calculations on Sn2Rh3S2and Pb2Rh3S2.

Inclusion Behavior of β‐Cyclodextrin with Bipyridine Molecules: Factors Governing Host‐Guest Inclusion Geometries

The 1:1 complexation of beta-cyclodextrin (beta-CD) with structurally similar bipyridine guests which lead to the formation of six inclusion complexes (1-6) of beta-CD with 4,4'-vinylenedipyridine, 2,2'-vinylenedipyridine, 1-(2-pyridyl)-2-(4-pyridyl)ethylene, 4,4'-ethylene-dipyridine, 4,4'-dithiodipyridine, and 2,2'-dithiodipyridine has been investigated comprehensively by X-ray crystallography in the solid state and by (1)H NMR spectroscopy and microcalorimetric titration in aqueous solution. The complex formation constants (K(S)) for the stoichiometric 1:1 host-guest inclusion complexation of beta-CD with the bipyridine derivatives were determined in aqueous solution by microcalorimetry and the host-guest inclusion geometries of the complexes were deduced from (1)H ROESY NMR spectroscopy. It transpires that the guest bipyridine molecules are included in the beta-CD cavity with a range of different inclusion geometries. In the solid state, the crystal superstructures for the beta-CD complexes 1, 4, and 5 are characterized by the triclinic crystal system (space group P1) commensurate with AAAA type supramolecular aggregation. By contrast, the beta-CD complexes 2, 3, and 6 display either monoclinic (space group P2(1)) or orthorhombic (space group C222(1)) crystal systems, characteristic of ABAB type supramolecular aggregation. The results demonstrate that the relative locations of the nitrogen atom positions and the bridge-bond links between the two pyridine rings in these bipyridine guests, not only lead to distinct crystal systems and space groups, but also to different binding geometries and thermodynamical parameters on complexation of the bipyridines with beta-CD. The knowledge obtained from this research improves our understanding of the molecular recognition and self-assembly processes exhibited by beta-CD, both in the solid state and in aqueous solution.

X-ray Diffraction Study of Ionic Liquid Based Mixtures

Crystal structures in N,N-diethyl-N-methyl-N-2-methoxyethylammonium tetrafluoroborate, [DEME][BF(4)], are determined by X-ray diffraction method. In [DEME][BF(4)]-based mixtures, various kinds of crystal structures and superstructures are induced by additives, i.e., H(2)O, CH(3)OH, C(2)H(5)OH, and C(6)H(6). Most of the crystal structures in the mixtures are related to that of pure [DEME][BF(4)], though unit cells in 1.1 and 6.1 mol % C(6)H(6) are different from the pure one. Further, [DEME][BF(4)]-C(6)H(6) mixtures require the two kinds of superstructures, where volume per [DEME][BF(4)] is contracted by a small amount of additives. Also, volume contraction and the coexistence of two kinds of superstructures are seen in 0.9 mol % H(2)O. The superstructures are derived from orientational or displacive modulations of [DEME][BF(4)] molecules. In spite of a small amount of additives, molecular interactions of [DEME][BF(4)] are influenced extensively.

The $$R{\overline{3}} c \to R{\overline{3}} m$$ transition in nitratine, NaNO3, and implications for calcite, CaCO3

The temperature dependences of the crystal structure and superstructure intensities in sodium nitrate, mineral name nitratine, NaNO3, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction. Nitratine transforms from $$R{\overline{3}} c\;\hbox{to}\;R{\overline{3}} m$$ at T c = 552(1) K. A NO3 group occupies, statistically, two positions with equal frequency in the disordered $$R{\overline{3}} m$$ phase, but with unequal frequency in the partially ordered $$R{\overline{3}} c$$ phase. One position for the NO3 group is rotated by 60° or 180° with respect to the other. The occupancy of the two orientations in the $$R{\overline{3}} c$$ phase is obtained from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x − 1, where S is 0 at T c and 1 at 0 K. The NO3 groups rotate in a rapid process from about 541 to T c, where the a axis contracts. Using a modified Bragg–Williams model, a good fit was obtained for the normalized intensities (that is, normalized, NI1/2) for the (113) and (211) reflections in $$R{\overline{3}} c\hbox {\,NaNO}_{3},$$ and indicates a second-order transition. Using the same model, a reasonable fit was obtained for the order parameter, S, and also supports a second-order transition.

Angular magnetoresistance oscillations in quasi-one-dimensional organic conductors in the presence of a crystal superstructure

We study the effect of crystal superstructures produced by orientational ordering of the ${\text{ReO}}_{4}$ and ${\text{ClO}}_{4}$ anions in the quasi-one-dimensional organic conductors, ${(\text{TMTSF})}_{2}{\text{ReO}}_{4}$ and ${(\text{TMTSF})}_{2}{\text{ClO}}_{4}$, on the angular magnetoresistance oscillations observed in these materials. Folding of the Brillouin zone due to anion ordering generates effective tunneling amplitudes between distant chains. These amplitudes cause multiple peaks in interlayer conductivity for the magnetic-field orientations along the rational crystallographic directions (the Lebed magic angles). Different wave vectors of the anion ordering in ${(\text{TMTSF})}_{2}{\text{ReO}}_{4}$ and ${(\text{TMTSF})}_{2}{\text{ClO}}_{4}$ result in the odd and even Lebed angles, as observed experimentally. When a strong magnetic field is applied parallel to the layers and perpendicular to the chains and exceeds a certain threshold, the interlayer tunneling between different branches of the folded electron spectrum becomes possible, and interlayer conductivity should increase sharply. This effect can be utilized to probe the anion ordering gaps in ${(\text{TMTSF})}_{2}{\text{ClO}}_{4}$ and ${(\text{TMTSF})}_{2}{\text{ReO}}_{4}$. An application of this effect to $\ensuremath{\kappa}\text{\ensuremath{-}}{(\text{ET})}_{2}\text{Cu}{(\text{NCS})}_{2}$ is also briefly discussed.

Exotic crystal superstructures of colloidal crystals in confinement

Colloidal model systems have been used for over three decades for investigating liquids, crystals, and glasses. Colloidal crystal superstructures have been observed in binary systems of repulsive spheres as well as oppositely charged sphere systems showing structures well known from atomic solids. In this work we study the structural transition of colloidal crystals under confinement. In addition to the known sequence of crystalline structures, crystal superstructures with dodecagonal and hexagonal symmetry are observed in one component systems. These structures have no atomic counterpart.