No description available.

Made available in DSpace on 2014-10-09T12:32:51Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:05Z (GMT). No. of bitstreams: 1 03526.pdf: 2946019 bytes, checksum: 162913e7d1135b3db6d5a5d5f9493dcc (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Quimica, Universidade de Sao Paulo - IQ/USP

Made available in DSpace on 2014-10-09T12:32:51Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:05Z (GMT). No. of bitstreams: 1 03526.pdf: 2946019 bytes, checksum: 162913e7d1135b3db6d5a5d5f9493dcc (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Quimica, Universidade de Sao Paulo - IQ/USP

No description available.

This thesis is concerned with the synthesis and characterisation of novel TCNQ (7,7,8,8-tetracyanoquinodimethane), TMTCNQ (2,3,5,6-tetramethyl-7,7,8,8-tetracyanoquinodimethane) and TCNQF4 (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) based zwitterionic D-1t-A materials (where D and A are electron donors and acceptors respectively) of which the methylated Z-~-(N-methyl-4-quinolinium)-a-cyano-4( 2,3,5,6-tetrafluoro)styryldicyanomethanide [CH3(4)Q3CNQF4] is a typical example. Synthetic modification of the donor moiety was also undertaken, resulting in a diverse range of pyridinium, quinolinium and benzothiazolium-based materials, which may have use in nonlinear optical research. For the quinolinium system an extensive range of both 2- and 4-substituted analogues have been prepared and their properties compared and contrasted. The solvatochromic behaviour of these zwitterions was investigated in detail by dissolution in a range of organic solvents and measurement of their longest wavelength charge-transfer absorption bands using UV/Visible spectroscopy, which revealed that the substituents have a marked effect upon their solvatochromic properties. Most of the adducts studied display highly negative solvatochromism as the solvent polarity increases, in which their absorption maxima are linearly related with the normalised ENT values for the Reichardt dye. However the fluorinated quinolinium and pyridinium derivatives exhibit an unusual aggregation-induced reverse solvatochromism effect. The negative halochromic behaviour of selected zwitterions has also been investigated, with a hypsochromic shift of the longest wavelength CT absorption band being observed upon addition of electrolytes. Increased polarisation within the fluorinated R(4)Q3CNQF4 and R(2)Q3CNQF4 adducts has been indicated by solution state dipole moment measurements indicating greater nonlinear optical potential. However this increased polarisation has also been shown to be a major cause of the limited stability of these materials to photo-oxidation. The behaviour of the R(4)Q3CNQF4 and R(2)Q3CNQF4 zwitterions on the subphase and their resultant Langmuir-Blodgett film forming ability was also studied. However unlike the TCNQ-based materials the fluorinated adducts have been shown to be poor LB film forming materials.

No description available.

No description available.

No description available.

No description available.

Homogeneous single C-S-H gels have been prepared for the investigation of alkali binding potential and crystallisation. A distribution coefficient, R_d, was introduced to express the partition of alkali between solid and aqueous phases at 25°C. R_d is independent of alkali hydroxide concentration and depends only on Ca:Si ratio over wide ranges of alkali concentration. The trend of numerical values of R_d indicates that alkali bonding into the solid improves as its Ca:Si ratio decreases. Reversibility is demonstrated, indicating a possibility of constant R_d value of the material. Al has been introduced to form C-A-S-H gels and their alkali sorption properties also determined. Al substituted into C-S-H markedly increases R_d, indicating enhancement of alkali binding. However, the dependence of R_d on alkali concentration is non-ideal with composition. A two-site model for bonding is presented. Crystallisation both under saturated steam and 1 bar vapour pressure has been investigated. It has been shown that heat treatment by saturated steam causes crystallisation of gels. The principal minerals obtained were (i) C-S-H gel and Ca(OH)₂ at ~55°C, (ii) 1.1 nm tobermorite, jennite and afwillite at 85-130°C, and (iii) xonotlite, foshagite and hillebrandite at 150-180°C. Properties of crystalline C-S-H were also reported for reversible phase transformation, pH conditioning ability, seeding effect and solubility. At 1 bar pressure, crystallisation is slower than in saturated steam due to lower water activity. Tobermorite-like nanodomains develop during reaction at low Ca/Si ratios. In some Ca-rich compositions, Ca(OH)₂ is exsolved and occurs as nano-sized crystallites.