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7/31/2019 TNH CHT QUANG HC CA H KEO
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TNH CHT QUANG HCCA H KEO
Trn LM NhnNguyn Th Minh Khoa
Hunh Vn ng
http://www.ctu.edu.vn/7/31/2019 TNH CHT QUANG HC CA H KEO
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Khi nh sng chiu qua h phn tn ta c th
thy cc hin tng sau: S khc x tia sng bi cc ht ca pha phn tn
S truyn tia sng qua h
S phn x tia sng bi cc ht ca pha phn tn S phn tn tia sng
S hp th tia sng bi pha phn tn chuyn
quang nng thnh nhit nng
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I. S PHN TN NH SNG
John Tyndall(1820 1893)
1. Hiu ng Tyndall
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2.S phn tn nh sng
Nm 1857 nh bc hc Faraday v sau nm 1869 Tyndall lu n hin tng m c. l hiu ng Tyndall.Hintng ny ch quan st c khi bc sng nh sng ln
hn kch thchtca pha phn tn. Nubc sng nhhnkch thc ht th xy ra hin tng phn x.Nguyn nhn:trngintca nh sng lm phn cc hacc nguyn t v phn tca mi trng. S phn cc ha xy
ra vitnsbngtnsca nh sng iti v cc nguyn t,phn tt n tr thnh ngun pht sng l nh sng phn tn.
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c tnh ca nh sng phn tn
Truyn theo mi hng
Cng ca nh sng phn tn theo cc
hng khc nhau l khc nhau nh sng phn tn thng b phn cc
i vi cc ht b th nh sng phn tn theo
gc 0o v 180ohon ton khng phn cc, cnnh sng phn tn theo gc 90ol phn cchon ton
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3. Phng trnh Rayleighv s phn tn nh sng
Nm 1871, nh vt l hcRayleigh thit lpphng trnh v s phntn nh sng cho cc h
phn tn gm cc ht hnhcu, khng dn in v cbn knh r 0,5 vi nng ht nh tc l cc htcch nhau tngiln.
opt Iv
nn
nnI
4
2
2
2
2
1
2
2
2
13.
24
Ipt
, Io
: cng nh sng phn tnv nh sng tin1, n2: chit sut ca pha phn tnv mi trng phn tn: nng htv: th tch ca mt ht
: bc sng nh sng ti
Lord Rayleigh(1842 1919)
(V.1)
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4. Cc yu t nh hng n s phn tn nhsngca h keo
S phn tn nh sng ph thuc vo chit sut
S phn tn t l thun bc hai vi th tch ht
S phn tn ph thuc vo bc sng nh sngDo cng nh sng phn tn t l nghch bc bn vi bcsng nn bc sng cng nh th b phn tn cng mnh vngc lai.
022
2
1nn H khng phn tn nh sng (nh tng ca
glycerin trong carbon tetra clorua c lmbn bng natri oleat th trong sut)
constv .
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Nm 1760, Lambert nghin cu s ph thuc ca cng nh sng su khi i quamt mi trng no v thit lp c phng trnh:
Trong : I,Io: cng nh sngtia l v tia tik: l h s hp th dung dchl: b dy ca mi trng nghin cu
Theo nh lut lambert th nu dyca mi trng tng ln heo cp scng th cng ca tia l gimtheo cp s nhn
I = Ioe-kt (V.2)
II. S HP TH NH SNG
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Sau nh bc hc Beer xc nh rng: h s hp th ca dung dch c dung mikhng mu v trong sut t l vi nng mol ca cht tan, tc l:
k = KC (V.3)
Trong : K l h s hp th mol.
C l nng mol ca dung dch
Th V.3 vo V.2 ta c phng trnh Lambert Beer:
I = Ioe-KCl (V.4)
Ly ln 2 v ca phng trnh:
KClI
Io ln (V.5)
I
Io
ln: mt quangca dd k/h l E (cn gi l tt hay hp th
T s c gi l trong sut tng i ca dung dchI
Io
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Bin i (V.4) ta c KCl
o
oKCl
o
KCl
o
eI
IIe
I
Ie
I
I
111 (V.6)
o
o
I
II c gi l hp th tng i ca dung dch
H s hp th mol K l mt hng s, l i lng c trng cho cht cho.Nu chn C= 1, l = 1 th
I
IK oln
Tc l K chnh l mt quang ca
dd khi nng mol v b dy calp dd l n v
K khng ph thuc vo nng nhng bin thin theo bc sng ca tia ti, nhit v bn cht ca dung mi. l Lambert khng ch ng vi dung dch thc mng vi c h keo c nng long v b dy ca lp dd nh.
Kch thc ht nh hng n s hp th nh sng gin tip qua s phn tn nh sng.Do s phn tn nh sng, mt phn nh sng trng i qua h mt i v mt phn bc xlm cho chng ta tng l s hp th. V vy phng trnh (V.4) c vit li nh sau:
I = Ioexp[-[K+F( r )]C.l]
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III. MU SC CA H KEO
hng ngc (cht
ln l Fe)
Mu ca cc loi qu{ l do s c mt trong mt lng v cng nh kim loinng v cc oxit ca chng trng thi phn tn keo
Ngc bch (mu xanh
do Crm)
Peridot
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Mu sccah keo cckzphctp .N phthuc vo bncht ca pha phn tn, mi trng phn tn, phn tn,hnh dng,cuto v phng quan st cngnhhngnmu cah keo.
Cc sol khng mu m pha phn tn l kim loi khng hpth
chn lc cc tia sng th khi chiu nh sng thngthng cmu da cam, cn chiu sng ngang th mc mu xanh datri. Tuy nhin, cng c nhiu sol kim loi c mu l do shpthchnlc cc tia sng.
Mu scca sol kim loi cngcckz phc tp. l do s
hp th nh sng bi cc ht kim loi v mt phn quangnngbin thnh hitnng. Bn cnh kim loivahpthmnh nh sng liva phn tn mnh nh sng
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IV. CC PHNG PHP QUANG HC NGHIN CU H KEO
Ngy nay cc phng php quang hc l phngphp ph bin nht xc nh kch thc, hnhdng v cu to ca h keo. V cc phng php nythng nhanh chng v tin li, cho kt qu chnhxc. Mt s phng php thng dng hin nay l:
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Knh siu hin vi
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S khc bit gia knh siu hin vi v knh hin vithng
Knh hin vi thngS quan st tin hnhnh nh sng xuyn qua
vt. Do ht c mu tiv th trng c musng.
Knh siu hin viThtrng th ti v nhsng t ngun khng
p vo mt ngiquan st cn cc htkeo th sng v n phntn nh sng.
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1. Phng php siu hin vi: Nm 1903,Zicdentoff v Zsigmondy pht minh ra phng
php knh siu hin vi c th m t bng hnh sau:
Richard Zsigmondy
(1865 1929)
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iu kin s dng phng php siu hin vi
Khong cch gia cc ht phi ln, ln hn cc phn chitca knh hin vi (khong cch nh nht gia hai im m knhhin vi c th quan st c) tc l nng ht phi nh.Nu khng cc ht dnh li, ta khng phn bit c.
Kch thc ht cng khng qu b hay qu ln. Nu cc htqu b th cng nh sng phn tn qu b, nu qu lnth phn x xung quanh u gy kh khn cho vic quan st.
Chit sut ca pha phn tn v mi trng phn tn phi
ln. Nu khng th cng nh sng yu khng th nhn rc.
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S ng i ca nhsng qua knh t quang
n:s ht trung bnh c trong h.
V: th tch h phn tn
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Bn canh knh siu hin vi, ngi ta cn sdng knh siuvi c knh t quang cho thtrngti. l mtthu knhcctmm trn v cc b th cm. Nguyn tc l
tia sng tdiithng vo knh t quang rihit vomtimnm trong cuvet chahcn nghin cut trnknh t quang. Do mtdica knh t quang c mt mngche hnh trn nn cc tia sng khng th xuyn qua n i vo ng knh c v ch c nhng tia p vo knh
nhng bn ngoi mng l i ln qua cuvet (hnh).Knh nyr, ngin v c thlp vo btcmt knh hin vi no. Da vo phng php siu hin vi ngi ta c th m
csht c trong mtth tch xc nh. Tuy nhin, vicxc nhshtphicthchinnhiuln v ly gi trtrung bnh v cc ht keo lc no cng c chuyn ngBrown.
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Nu bit c th tch ca h keo th ta tnh cnng ht:
Vi n : s ht trung bnh c trong hV: th tch h phn tn
Nu bit c khi lng ring ca ht l dv khi lng mca phaphn tn trong mt lit dd th ta c th tnh c kch thc cc httrong mt n v th tch nghin cu:
trong : l th tch ca mt ht
V
n
ndvm nd
mv (V.9) (V.10)
v
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Nu ht keo l hnh cu ta c th tnh c bn knh ca ht keo:
Nu ht hnh lp phng ta tnh c kch thc l ca ht:
32
4
3
3
4
nd
mr
nd
mrv
(V.11)
33
nd
m
lnd
m
lv (V.12)
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Phng php siu hin vi khng nhng xc nh c kch
thc trung bnhca ht m cn c th bit c hnh dnght.
Nu nh sng quan st c trong th trng lp lnh thchng t n bt i xng. Nguyn nhn l do cc ht khng
phi hnh cu b nh hng ca chuyn ng Brown nn bnh sng chiu vo khc nhau v din tch b chiu sng v ntruyn vo mt ta lng nh sng khc nhau thi im khcnhau.
Nu cc ht quan st c lng nh sng u khnglp lnhth chng t l dng kh i xng.
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Gn y, ngi ta s dng knh siu hin vi dng. Knh nyc th xc nh nhanh chng s ht trong mt n v th
tch lyosol hay aerosol. Nguyn tc hot ng: lyosol hay aerosol chy dc theo
rnh cuvet 2 c t cng trc vi ng knh hin vi 5. Miht i vo vng chiu sng bi ngun sng 3 cho mt msng. Tng s m sng c th m c d dng. Chia
s m sng cho th tch lyosol hay aerosol m b phn 1o c, t tnh c nng ht. u im:loi b hu ht cc nhc im ca knh siu
hin vi v tit kim c thi gian.- T ng ho vic m bng cch: knh c thay i th
no nh sng i t cc ht chiu vo catod ca mt nkhuch i nh sng. Mt m sng i qua cuvet s tonn mt xung in m sau khuch i th c ghi bi mtmy m
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2. Phng php knh hin vi electron Ngi ta thay th nh sng bng mt chm electron nhanh.
Dn ti vic tng cng kh nng phn chit ca knh v cth chp c nh ca ht keo. di sng ca chmelectron l l 0.02 0.05 , xp x bng kch thc nguyn t.Khi kh nng phn chit ca knh hin vi electron c
nng ln t 5 10 . Hnh nh thu c trn mn huznhquang c th chp nh c v sau phng i nh lnnhiu ln.
Do electron d b phn tn v d b hp th nn vic hi t cc
tia sng phi dng in trng hay t trng gy nn nh cccun in t. gim bt s phn tn electron, bn trongknh hin vi electron phi l mi trng chn khng.
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u im:C th thy c cc ht rt nh vi
tt c cc c tnh v hnh dng v cu to.
Nhc im: Phi s dng t m, mu chun bphc tp v phi m bo mi trng chnkhng cao. Ngoi ra, mu t trong chn khng
nn khng th quan st cc ht keo chnh trongh c m ch c th quan st na trong ktta kh.
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3. Phng php o c
Phng php ny da trn s phn tn nh sng ca h keo. Xc nhcng m c ca h cho c th xc nh c kch thc ht keohay nng pha phn tn. Khi phng trnh Rayleigh c th c vitli nh sau:
vkCIvvIkIvkIpt 0002
42
2
2
1
2
2
2
131
224
nn
nnk
vC .
Vi
v
(V.13)
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Cc i lng trong phng trnh Rayleigh bit, ch cnxc inh nng th tch ca pha phn tn C v cng tuyt i ca tia ti v tia phn tn (I0,Ipt) c th tnh c thtch trung bnh ca ht v. Tuy nhin, vic xc nh cng tuyt i ca tia ti v tia phn tn i hi dng c kh phctp nn n gin ngi ta dng mt phng php khc l phng php o c bng mt c k
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4
6
8 9
10
7
5
2
31
S c k Kleinmann
1.Ngun sng
2,3.Cuvet ng dung dch
4,5.mn che di ng
6,7.Thi thy tinh
8,9.Lng knh
10.Th knh
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i vi phng php o c ta tin hnh o m cca dung dch nghin cu so vi m c ca dung dchchun ( bit kch thc ht).T tnh ra kch thc httrong dung dch nghin cu. iu kin p dng phngphp ny l nng th tch ca pha phn tn trong hai dungdch l bng nhau.
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ckgm hai cuvet thy tinh hnh trginght nhau,mtng ng dung dch nghin cu v mtng ngdung dchchun. Cho chm nh sng mnhchiu ngangvo hai cuvet hnh tr. Khi ta quan st chiungTyndall. Phn dung dchbchiu sng haing hnh tr
c th iu chnh c bi mng chn. nh sng phntn bi cc dung dch cha trong cuvet i qua hai thithy tinh nhng vo trong dung dch cng su(nhm mc ch loi tr s phn x nh sng trn ccmt khum ca dung dch trong cuvet). T hai cuvet, nhsng phn tn hng v th knh nh h thng lngknh.th knh nm pha trn hai cuvet c chia ra lmhai phnnhn nh sng phn tn t hai cuvet ti.
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Cch xc nh: Khi nng hoc h cc mn chn tc l ta iuchn cng sng hai na th knh bng nhau. Ngha lcng nh sng phn tn ca dung dch nghin cu bngcng nh sng ca dung dch chun. Khi ta c:
Nu bit c kch thc ht trong dung dch chun th d
dng bit c th tch trung bnh ca dung dch nghin cu
'0201hIkCVhIkCV
1
2
' V
V
h
h(V.14) V.15
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Lu :Phng php ny ch p dng tt cho h n phntn. Ngoi ra, bc sng trong phng trnh Rayleigh ch
khng ph thuc vo kch thc ht i vi cc sol c phn tn cao nn phng php ny ch p dng cho h dth c phn tn cao.
T phng php o c ta c th xc inhj c nng th tch ca h keo nghin cu. Vi iu kin l dung
dch chun v h keo nghin cu phi cha cc ht c cngbn cht v cng kch thc. Khi pt (V.15) c th vit li:
h
h
C
C
hChC
'
'2
1
21
(V.16)
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Hin nay, ngi ta s dng c k quang in. Bng cch xcnh cng dng nh sng i v i tc dng vo t bo
quang in ca nh sng phn tn t dung dch keo nghincu. Khi phng trnh (V.15) v (V.16) c th vit li nhsau:
Tm li, phng php ny ch thch hp vi sol khng mu.
i vi sol c mu v nht l sol kim loi th phng phpny khng p dng c. V s phn tn nh sng ca h nykhng tun theo phng trnh Rayleigh
2
1
2
1
' C
C
V
V
i
i