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5.2 solvent thf interaction with zno 67is found at z ∼ 0.5 nm [110]. Away from this layer a lowdensity region of width ∼ 2 nm follows.The present THF/ZnO case is consistent with the abovepicture. The region C identified in our investigation correspondsto the densified one ( i.e. wetting layer) and L ′to the low density region. At variance with the cyclohexanecase we do not observe sizable exponential fluctuationsand we attribute this behavior to the actual bondingbetween the molecules and the hard substrate. The THFmolecules have the same orientation on the ZnO hard surfaceand gives rise to a softer surface composed by methylenicgroups (-CH 2 ) that does not induces fluctuations on the remainingliquid.5.2.2.2 ZnO/THF structure factorsTo further investigate the order of the system in eachslice, we calculate the average structure factor (defined inchapter 2) of the oxygen atoms along the x and the y directions.Accordingly, in order to investigate the local crystallinity,the structure factor as a function of λ = 2π/q iscalculated by repeating the calculations in different regionsof the system. As for the region C, containing the wettingTHF layer, there are peaks at λ = 3.25 Å and λ = 5.20Å for S(λ) along the x and y directions, respectively. Theseλ values correspond to the lattice periodicity of our ZnOsurface, showing a crystalline order in the wetting layerinduced by the ZnO surface. By considering the slice justabove the wetting layer (region L ′ ), the order is lost and aflat low-value S(λ) profile is found (see Figure 5.7, right).The differences in the S(λ) profiles along x and y directionsare not sizable and it can be concluded that, exceptfor the wetting layer, there is no order in THF even close tothe interface. This analysis further confirms that, in termsof structure, the THF/ZnO interface is sharp.5.2.2.3 ZnO/THF energeticsThe next analysis involves the energetics of the ZnO/THFsystem by calculating the adhesion energy within the system.To this aim is considered a plane (hereafter labeledas A/B) that divides the system into two parts, A and B,and the work (w) necessary to rigidly separate them at in-
68 interaction between tetrahydrofuran solvent and zinc oxidezyxzxyFigure 5.7.: Structure factor in the x (top) and y (bottom) directionfor the wetting layer C (left) and the liquid THF close tothe surface L ′ (right).creasing distance z is calculated. At infinite distance, thiswork is by definition the adhesion energy γ A/B of the twoparts A e B. In the case where a molecule is cut by theplane, the whole molecule is attributed to the part (A orB) containing its oxygen. The calculated γ A/B is directlyrelated to energies of the generated surfaces (σ A and σ B );in particular, γ A/B = σ A + σ B . We consider three cuts (seeFigure 5.6): (i) L/L, separating two halves of the bulk liquid;(ii) C/L ′ , separating the crystalline layer C from theneighboring liquid THF layer (L ′ ); (iii) Z/C, separating theZnO crystalline surface (Z) from the wetting layer (C).The L/L work of separation (w L/L ) as a function of thedistance is reported as red curve in Figure 5.8 and it isnormalized to the asymptotic value. This work varies untilthe two semi-bulks are interacting. At distances largerthan the interaction range (z 0 ∼ 7 Å) the work reachesthe asymptotic value γ L/L . Because of the statistic distributionof molecules in the liquid phase, γ L/L is found toslightly depend on the position of the cut. For this reasonwe averaged the results over different cuts and we find
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Università degli Studi di Cagliari
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A C K N O W L E D G M E N T SI woul
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example of a novel class of systems
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C O N T E N T S1 introduction 11.1
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L I S T O F F I G U R E SFigure 1.1
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List of FiguresxiiiFigure 2.15 Init
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List of FiguresxvFigure 4.6Figure 4
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Figure 5.7Figure 5.8Figure A.1Figur
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2 introduction1-3 eV) and the trans
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4 introductionorder in such a compl
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6 introductionprocesses that need t
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8 introduction1.2 physical factors
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10 introductionrecovered by the int
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12 introductionA cheap and environm
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14 introductiondensed phases [63, 7
Page 36 and 37: P 3 H T - P O LY ( 3 - H E X Y LT H
Page 38 and 39: 2.1 mechanism of assembling and mor
Page 40 and 41: 2.2 p3ht assembling and intermolecu
Page 42 and 43: 2.3 p3ht crystalline bulk phases 23
Page 44 and 45: 2.5 nanocrystalline p3ht 25Figure 2
Page 46 and 47: 2.5 nanocrystalline p3ht 27Table 2.
Page 48 and 49: 2.6 conclusions 29Figure 2.13.: Ini
Page 50 and 51: P O LY M E R / S E M I C O N D U C
Page 52 and 53: 3.3 adhesion of a single p3ht molec
Page 54 and 55: 3.4 p3ht/zno interface 35surface (t
Page 56 and 57: 3.5 p3ht/zno interface: low deposit
Page 58 and 59: 3.6 p3ht/zno interface: high deposi
Page 64 and 65: 3.7 effective model for the transpo
Page 66 and 67: 3.8 conclusions 47As for the low te
Page 68 and 69: T E R N A RY Z N O / Z N P C / P 3
Page 70 and 71: 4.1 self assembling of znpcs on zno
Page 72 and 73: 4.2 polymer interaction with znpcs
Page 74 and 75: 4.3 electronic and optical properti
Page 76 and 77: 4.3 electronic and optical properti
Page 78 and 79: 4.4 conclusions 59ties. The absorpt
Page 80 and 81: I N T E R A C T I O N B E T W E E N
Page 82 and 83: 5.2 solvent thf interaction with zn
Page 84 and 85: 5.2 solvent thf interaction with zn
Page 88 and 89: 5.3 conclusions 69γ L/L ∼ 0.112
Page 90 and 91: C O N C L U S I O N SIn this thesis
Page 92 and 93: M O L E C U L A R D Y N A M I C SAa
Page 94 and 95: A.1 molecular dynamics 75a.1.2The t
Page 96 and 97: A.2 the force field 77Finally, τ t
Page 98 and 99: A.2 the force field 79Waals interac
Page 100 and 101: A.3 methods 81tional Theory (DFT) l
Page 102 and 103: B I B L I O G R A P H Y[1] http://w
Page 104 and 105: ibliography 85[17] J. D. Servaites,
Page 106 and 107: ibliography 87Zakeeruddin, and M. G
Page 108 and 109: ibliography 89Phys. Chem. Chem. Phy
Page 110 and 111: ibliography 91[65] D. J. Binks and
Page 112 and 113: ibliography 93cells,” Energy Envi
Page 114 and 115: ibliography 95[97] C. Ingrosso, A.
Page 116 and 117: ibliography 97298.15 k,” Journal
Page 118 and 119: ibliography 99charges. am1-bcc mode
Page 120: colophonThis document was typeset u
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