We probe the local and global structure of spin-coated colloidal crystals via laser diffraction measurements and scanning electron and atomic force microscopies, and find that they are unique three-dimensional orientationally correlated polycrystals, exhibiting short-range positional order but long-range radial orientational correlations, reminiscent of-but distinct from-two-dimensional colloidal hexatic phases. Thickness and symmetries are controllable by solvent choice and spin speed. While the polycrystallinity of these colloidal films limits their applicability to photonics, we demonstrate their feasibility as templates to make crack-free magnetic patterns. DOI: 10.1103/PhysRevE.77.050402 PACS number͑s͒: 82.70.Dd, 64.70.pv, 64.75.Yz The self-assembly of colloidal microspheres has been used to address the fundamental questions of how materials crystallize ͓1-6͔ or fail to crystallize ͓7-9͔. Micrometer-scale colloidal crystals can be used as a template that, using further processing methods, can be used to create photonic materials ͓10-12͔, optical sensors ͓13͔, and antireflection coatings ͓14͔. However, the high density of missing-sphere defects and cracks in photonic crystals produced via self-assembly ͓15͔ remains a serious limitation, and thus the study of colloidal defects ͓16͔ is an active area of research. Spin-coating of colloidal suspensions is the quickest and most reproducible method to make large-area colloidal crystals. While spin-coating has been proposed to fabricate single crystals for photonic applications ͓17,18͔, the symmetric radial optical interference patterns observed are unexpected for single crystals. We find here that spin-coated colloidal films are indeed neither single crystals nor powder polycrystals, but are in fact a unique polycrystal phase. While true singledomain sizes are ϳ10 m, there is orientational correlation on the centimeter scale. Our results demonstrate a novel crystal packing strategy by which long-range orientational order develops in the absence of long-range positional order, reminiscent of two-dimensional colloidal hexatic phases ͓19,20͔, and leading to crack-free crystals. Distinct from colloidal hexatic phases, our polycrystals exhibit centimeterscale orientational order, which arises due to the spinning axis and can be produced with fourfold, sixfold, or mixed symmetries for a range of thicknesses as a function of spin speed. The electrodeposition of magnetic material through colloidal polycrystals demonstrates their feasibility for material templating applications.The standard technique to make large-area close-packed crystals is controlled ͑vertical͒ drying, utilizing capillary forces ͓21-23͔ to direct self-assembly. Other external shear ͓24͔, electric ͓25͔, electrohydrodynamic ͓26,27͔, and gravitational forces ͓28͔ have also been used. Making dried colloidal crystals with these methods is slow, taking from hours to days. Spin-coating has been shown to be a robust technique ͓17,18,29,30͔ to make large-area colloidal crystals in minutes. In this work, we ...

Specimens of aerial and hydraulic lime-based mortars to be used in restoration works were prepared, hardened and subjected to different environments in order to study their mechanical behavior and durability. Outside exposure, weathering cycles in a climatic chamber, SO 2 -rich environment, freezing-thawing cycles and indoor exposure were selected to expose (as control group) the mortars.Flexural and compression strength tests were performed at 7, 14, 21 and 28 days. Porosity values and SEM-EDAX analysis were used to evaluate the microstructural changes.Flexural strength has been strongly influenced by the RH of the environments. Outside exposure improves, in general, the compressive strength, whereas SO 2 -chamber only provides the strength in hydraulic specimens. Porosity reduction has been related with a strength increment.In climatic chamber, the porosity increment matches a gradual higher degree of alteration. A strength reduction has been determined through a fracture mechanism using the cracks of climatic alteration. In SO 2 -chamber, sulfation appears as a surface phenomenon, giving gypsum in aerial specimens and gypsum and syngenite in hydraulic specimens, as SEM/EDAX confirms. Freezing-thawing cycles showed a high destruction capacity. Hydraulic specimens endured better durability tests than aerial specimens: a discussion on the mortar durability was also introduced.

Two polycarboxylate ether copolymers were assessed as superplasticizers (SPs) for hydrated lime pastes modified with two reactive compounds, nanosilica (NS) and ceramic metakaolin (MK). Characterization of the molecular structure of the SPs by Size Exclusion Chromatography, XRD, FTIR and MALDI-TOF (Matrix Assisted LaserDesorption Ionization Time-of-Flight) mass spectrometry was performed. The structures of the polymers were seen to be star-and worm-like shapes. A close relationship was found between the molecular architecture and the flowability of the pastes, being the star-shaped plasticizer the most efficient. Zeta potential assessment allowed us to elucidate a steric hindrance as the main action mechanism for these polymers. The large specific surface area of nanosilica led to a large SPs consumption as compared with metakaolin with lower surface area. However, SPs in MK-lime samples were attached favourably on the C-S-H and aluminate hydrates, so that the dispersing action was greater with respect to NS-lime suspensions.2

39The effect of individual and combined addition of both nanosilica (NS) and 40 polycarboxylate-ether plasticizer (PCE) admixtures on aerial lime mortars was studied. 41The sole incorporation of NS increased the water demand, as proved by the mini-spread 42 flow test. An interaction between NS and hydrated lime particles was observed in fresh 43 mixtures by means of particle size distribution studies, zeta potential measurements and 44 optical microscopy, giving rise to agglomerates. On the other hand, the addition of PCE 45 to a lime mortar increased the flowability and accelerated the setting process. PCE was 46shown to act in lime media as a deflocculating agent, reducing the particle size of the 47 agglomerates through a steric hindrance mechanism. Mechanical strengths were 48 improved in the presence of either NS or PCE, the optimum being attained in the 49 combined presence of both admixtures that involved relevant microstructural 50 modifications, as proved by pore size distributions and SEM observations. 51 the technical characteristics of the final product and/or addressing environmental issues 58 [3][4][5]. The addition of nanosilica (NS) has attracted increasing interest because of the 59 filling effect, which improves the particle size distribution, thus reducing porosity, and 60 the pozzolanic reaction between NS and calcium hydroxide (CH) yielding calcium 61 silicate hydrates (C-S-H). These actions result in enhanced mechanical strength [6][7][8]. 62The filling of the interparticle space leads to a denser packing and reduces the water 63 demand, as there is no need to fill the space with water. In this case, the use of a 64 superplasticizer is required in order to guarantee workability [9]. Furthermore, the 65 strong tendency of NS to agglomerate also may make it necessary to use a dispersing 66 additive in order to overcome this problem and to ensure enough reactive surface for the 67 filling effect and C-S-H formation [7,10,11]. Dispersing additives are the so-called 68 plasticizers or superplasticizers, which have a water reducing action on cement 69 materials. When superplasticizers are added, workability at a constant water/cement 70 ratio is improved. Alternatively, the same workability as that of plain cement paste can 71 be reached with an outstanding reduction in water content. In the latter case, cement 72 materials with higher mechanical strengths can be obtained. The adsorption of the 73 plasticizer molecules on the solid particles, either by modifying the surface charge (zeta 74 potential) of the particles, thus increasing the electrostatic repulsion, or by steric 75 hindrance, causes a dispersing action, which has been claimed to be responsible for the 76 increase in fluidity of the cement paste [12]. The interaction between the 77 superplasticizer and the particles of the binder could be affected by the presence of 78 4 mineral additions (such as NS, silica fume or fly ash), which means that the 79 compatibility between them needs to be studied [13]. 80 81The interest in usi...

Specimens of aerial and hydraulic lime-based mortars to be used in restoration works were prepared, hardened and subjected to different environments to study their compositional changes during setting, hardening and exposure to environment. Outside exposure, weathering cycles in a climatic chamber, SO 2 -rich environment and indoor exposure (as control group) were selected to expose the mortars. XRD, FTIR and TG-DTA analyses were performed at 7, 14, 21 and 28 days to determine the chemical and mineralogical composition, as well as the formation of the degradation products. Outside and SO 2 -chamber exposures and increasing the relative humidity allowed faster carbonation (enhancing CO 2 (g) dissolution) and hydration of hydraulic compounds. In SO 2 -chamber, sulfate attack appears as a surface phenomenon, giving: gypsum in aerial specimens and gypsum and syngenite in hydraulic specimens.